When pricing out a new system, the power supply unit is usually the component at the bottom of the list. We admit, it’s hard to get excited about the PSU. Jacob Freeman, product manager at EVGA, thinks the PSU’s role in gaming, overclocking, and enthusiast computing is underrated. “Due to the nature of the device, it is not easy to measure the performance of the power supply without expensive equipment, thus some users may buy PSUs that offer low efficiency, or have low quality components that can cause all sorts of issues from system crashes to power supply failure.”
No, the PSU doesn’t directly impact the performance of your PC, but it does feed the components that do make that impact. It’s very possible to get it wrong and never know it. Buying too much power wastes energy, and buying an underpowered PSU may prevent your computer from booting, fail whenever you hit it with a load, and limit your overclocking potential and future upgrade options. Read on to determine what to buy when it comes time to replace your power supply.
Do You Really Need A New PSU?
If your current PSU is a few years old, then the answer is probably “Yes.” The problem is, as it ages, your PSU begins to suffer from capacitor aging, which occurs as the electrolytic capacitors in a well-used power supply drop as much as 10% to 20% of their initial wattage capacity per year of operation. MOSFETs also age (making them less capable of handling increasing ripple current), noise filtering slips, and the PSU slowly begins to overwork the voltage regulation circuits on the motherboard and elsewhere. Only very specialized equipment can detect these issues, so it’s always good to replace an old PSU before it actually fails.
You may find that your old PSU is just not capable of keeping up with today’s gear. To solve the problem of increasing current demands from the processor and other components, Intel came up with the ATX12V standard, which gave us the 4-pin power connector that dedicates +12VDC to the CPU. Most modern motherboards use an 8-pin CPU power connector to deliver more current to the processor. Although the 4-pin +12V CPU connector on older PSUs may not prevent an 8-pin connector motherboard from booting, it may limit your overclock potential and possibly shorten the CPU’s life span. Besides the connectors, there are other particulars of the ATX standard that may have effectively rendered your old PSU obsolete.
Spec Check
The ATX standard that defines power supplies in PCs has seen several major alterations since 2003’s ATX12V 2.0 revision, which mandates that a majority of the computer’s power be driven through the 12V rails. The revision also replaced the old 20-pin connector with a 24-pin ATX connector that feeds another 3.3V, 5V, and 12V circuit. SATA power connectors became standard, and efficiency targets became mandatory. An EU mandate and Intel’s ATX12V 2.0 revision required multiple 12V rails (each with independent overcurrent protection circuits) if a single rail would exceed 240VA, but some budget PSUs were able to drive them from a single transformer, which could starve components for current and reduce overall reliability. Quality PSUs employ dedicated transformers for each rail to deliver sufficient power.
In June 2004, Intel introduced ATX12V 2.01, which made a few minor tweaks, one of which was to scrub the −5V rail references from the specification. Less than a year later, ATX12V 2.1 marginally boosted the power of all rails, tweaked the efficiency requirements, increased the standby current of the 5V rail, and defined the typical power distribution for 450W PSUs. In 2005, we got version 2.2, which specified High Current Series wire terminals for ATX main power, the +12V power connector, and the 24-pin main and 4-pin +12V power connectors.
Revision 2.3 raised the recommended PSU efficiency to 80% (70% minimum), bringing computers into compliance with Energy Star 4.0 mandates, and decreased the 12V minimum load requirement, which lets PSUs run modern processors with very low power consumption during startup. The revision also removed the absolute overcurrent limit of 240V per rail, which let 12V lines deliver more than 20A per rail. Today, high amp 12V rails are a must-have for those who’re running high-end graphics cards.
In early 2008, the ATX 12V 2.31 revision capped the ripple/noise levels for the PWR_ON and PWR_OK signals at 400mV (millivolts). This revision also requires that the DC power must hold for more than 1 millisecond after the PWR_OK signal drops, clarifies country-specific input line harmonic content and electromagnetic compatibility requirements, and more. If your PSU doesn’t support the latest standard, or at least revision 2.3, then it’s time for a new one.
Why Good Enough Is No Good
A bad PSU only rarely becomes apparent when your system fails to power on, or worse, when sparks and smoke issue from its innards. But your PSU doesn’t have to fail in a spectacular fashion to cause lasting and irreparable damage to your other components. Like most things, you get what you pay for with PSUs. The voltage-regulating components on your motherboard, processor (Haswell processors in particular have on-die voltage regulation), and graphics cards work to compensate for ripple (the minor variance that occurs in the DC output voltage) generated by the PSU. The latest ATX specification allows for up to plus or minus 120mV of ripple on the +12V rail, and voltage regulation can introduce an additional 5% of variance either way. Cornercutting PSUs may meet the specification, but they will put more stress on the inductors and capacitors of the aforementioned parts.
Better To Be Smart Than Loyal
Before you dismiss a PSU that isn’t a brand you trust or recognize but otherwise ticks all the right boxes, keep in mind that there are several vendors that simply slap their stickers on PSUs manufactured by another company. You can even determine virtually any PSU’s original manufacturer thanks to the 80 PLUS Certification Verification And Testing Report. Every 80 PLUS PSU gets one of these reports, and the organization isn’t keen on retesting PSUs just because they sport a repainted enclosure or another manufacturer’s logo. Start by visiting bit.ly/1nIrKUw and clicking the manufacturer (on the sticker). Find and click the link to the model in question to bring up its report. Next, make note of its Ecos ID# in the chart at the top left corner of the report. If the number ends with a decimal point, such as 1234.2, then it’s likely a rebranded PSU. You can verify this by performing a Google search for “ecos id# 1234 site:plugloadsolutions.com” (replace “1234” with the Ecos ID# you found on the report, without the decimal. The resulting hits will take you to the identical reports, with the respective manufacturer and model fields changed to indicate the rebrand. The manufacturer of the model that features an Ecos ID# without a decimal point is the original one.
We don’t have an issue with rebranded PSUs, and you shouldn’t either. Sometimes a company will use another manufacturer’s PSUs to flesh out its own lineup and offer more competitive pricing. The practice is so prevalent that you might even be running a rebranded PSU in a system or two of yours. In most cases, these companies know that putting their logo on a low-quality device will ultimately come back to haunt them in the form of RMAs, support calls, and lost customers. It just goes to show that most of the time, a well-known brand means less than the quality of the components inside the PSU.
You also shouldn’t dismiss a PSU just because you’ve never heard of the manufacturer. Some lesser-known companies have spent several years, even decades making PSUs for OEMs or rebrands for other companies. Do a little research into the company and you may be impressed with its résumé. Although many enthusiast PC parts companies offer a variety of products, such as mice, keyboards, cases, CPU coolers, and PSUs, others specialize exclusively in PSUs.
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| The 80 PLUS program defines the different efficiencies of PSUs. |
Calculating Wattage & Amperage
If you’ve determined that you could use a new PSU, the next thing you should do is hold off on picking it out until you’ve finalized the list of components that will constitute the rest of your system. That’s right, keep the PSU at the bottom of your parts list, but at the top of your list of priorities.
The best way to pick a PSU wattage is to add up some numbers. Start with your CPU and graphics card’s TDPs, making sure to multiply these numbers if you have more than one of either or both. For example, the Intel Core i7-5960X and the AMD FX-9590 have respective TDPs of 140W and 220W, and the AMD Radeon R9 290X and GeForce GTX 980 have respective TDPs of 290W and 165W. Any combination of the aforementioned parts has a combined TDP of between 305W and 510W. Fans, hard drives, SSDs, memory, the motherboard, and most other components consume comparatively little power, so we recommend adding another 100W to take care of them. Of course, if you’re running a dozen HDDs or another unique configuration, you may want to pad this number a little more. Overclocking can take a toll, as well, so you may need to do a little digging online to determine how much power your chosen components draw when overclocked. Some components, GPUs and CPUs alike, can double their rated TDP when you start pushing the voltage settings upward, so be generous here. As you can see, we’re already looking at a kilowatt PSU.
When calculating wattage, keep in mind that if you buy a PSU with just enough power to run your equipment, you may be fine, but the fan will be running faster and louder than if you had targeted a PSU with a little more breathing room. Opting for a PSU with a larger fan, such as 120mm or 140mm, can negate this issue somewhat due to its ability to move air using lower speeds.
If you don’t want to fuss with simple math, visit bit.ly/1hPNhZY to use eXtreme Outer Vision’s exhaustive eXtreme Power Supply Calculator Lite. (The $1.99 Pro version lets you calculate PSU wattages for up to six graphics cards, factor-in amperage values, and determine the performance of an uninterruptible power pupply). This calculator uses 90% of the TDP due to the fact that 100% utilization is extremely rare when running real-world applications. We also like that the calculator accounts for capacitor aging, so you can make sure to get a PSU that will run reliably for several years. There are other calculators out there, but most are too simplified to be worth using.
According to the eXtreme Power Supply Calculator Lite, we’ll need a 594W PSU to handle our test system, which consists of a stock-clocked Core i7-5960X, GIGABYTE X99-GAMING G1 WIFI motherboard, 16GB of ADATA DDR4-2400, a 240GB SSD, a Blu-ray optical drive, four 120mm fans, a closed-loop CPU cooler, and a PNY XLR8 GeForce GTX 780 Ti. When we connected our PSU tester, the system drew 460W from the wall with Prime95 and Aliens vs. Predator hammering the CPU and GPU. Not a bad estimate at all; a 600W PSU would even give us leeway for some minor overclocking.
Although wattage is important, the amperage your components draw from the 12V rail is just as crucial, especially as many high-end graphics cards demand close to 40A or more. You may need to do a little digging to determine how many amps your GPU requires, but make sure to factor this in when choosing a PSU.
Finally, when looking at wattage numbers for a PSU you plan to buy, make sure you’re basing your judgment on the continuous power number, sometimes referred to as average output. Peak wattage is usually the spec listed on the box, but the continuous power wattage can be significantly lower. Continuous power is also typically measured at a given temperature. Even the worst PSUs can maintain peak power on ice, but that’s not realistic. Commonly, 25 to 30 degrees Celsius is considered room temperature. At 40 and 50 C, PSUs are operating in servergrade conditions, and those will tend to have very reliable output in your home regardless of the temperature in your system.
Multi-GPU Certification
When shopping for a PSU, you may encounter AMD CrossFireX and NVIDIA SLI-ready logos. For the most part, PSUs that features these logos have undergone certification testing from the respective GPU makers. PSUs that lack these logos can still handle multi-GPU scenarios just as capably. To reiterate, you just need to make sure there are enough of the appropriate native PCI-E power connectors, high enough current on the 12V rail, and enough wattage to cover the respective power draw.
Buying A Resourceful PSU
Choosing a PSU with enough wattage and amperage is just the beginning. Efficiency is another important factor to consider, primarily because a more energyefficient PSU will save you money on your energy bills (albeit not much) and result in a system that runs cooler and quieter.
In the last several years, 80 PLUS has begun pushing PSU manufacturers to produce more energy-efficient devices. Currently, the program consists of six levels and corresponding logos. The baseline certification, simply “80 PLUS,” refers to PSUs that that are at least 80% efficient under 20%, 50%, and 100% loads. In these PSUs, 20% of the power drawn from the outlet is lost as heat under the corresponding loads. 80 PLUS Bronze, Silver, Gold, and Platinum-certified PSUs support 82%, 85%, 87%, and 89% efficiencies at 100% load, respectively (in addition to similar efficiencies at other loads). The newest classification, 80 PLUS Titanium, refers to PSUs that have been tested to operate at extremely high 90%, 92%, 94%, and 90% efficiency under loads of 10%, 20%, 50%, and 100%, respectively.
80 PLUS Bronze and higher PSUs meet the new Energy Star Version 5.0 Specification, which calls for PSUs to yield at least 85% efficiency at 50% of their rated output. Today, 80 PLUS Gold has become fairly mainstream; you can easily find good PSUs that support it at a variety of wattages and price ranges. For the most part, you will pay significantly more for a PSU that achieves Platinum or Titanium certification, and the energy you save won’t make much of a dent in your bill.
Another useful facet of energy efficiency ratings, especially for those looking to put the very best PSUs into their systems, is as a mark of quality. It takes a significant amount of advanced technology to convert and regulate power for PCs at 90% efficiency or better, so the PSUs that can do it tend to utilize the latest techniques and be manufactured with the best components. And you can bet you will pay for it.
Power factor correction, often shortened to PFC, is the technique PSUs use to ensure a majority of the current supplied from the outlet actually remains useful to the components that need power. There are two methods for achieving this, active PFC and passive PFC. In the latter, the PSU uses a capacitive filter at the AC input that effectively sacrifices some amount of the incoming power to make sure there’s always a minimum amount of usable current, regardless of environmental vibration. Active PFC, on the other hand, uses a circuit to monitor power factor and makes on-the-fly adjustments to keep up. As you might guess, active PFC PSUs are more efficient and preferable in most cases. Thankfully, they’re also very common, and the feature doesn’t add much cost to the PSU.
Digital signal processing (DSP, common in server PSUs) is another technique that high-end PSUs use to ease the stresses that afflict the component voltage regulation circuits. DSP-equipped PSUs, sometimes referred to as digital PSUs, let the different parts of the device communicate, resulting in significantly faster response times for load and voltage shifts. Other benefits of DSP-equipped PSUs include less ripple and reduced signal noise. Unlike active PFC, DSP adds a significant amount of cost to the PSU and typically only shows up as a feature on the highest-end PSUs.
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| The heavy-duty capacitors in your PSU will lose some of their performance as they age. |
Cabling Concerns
Generally speaking, if you’ve selected a new PSU that includes all of these features, then that PSU will more than likely have all the connectors you need to power your components. Multi-GPU users should make sure there is a sufficient number of 6+2-pin PCI-E connectors; bank on two (and in very rare cases, three) for each graphics card you intend to install. Numerous SATA power connectors are a must-have for those who plan to install a large bank of SSDs or HDDs.
Modular cabling, considered an enthusiast feature by some and an unnecessary voltage sacrifice by others, has also improved of late. Many modular cabling systems have opted for a hybrid design that pairs solid cabling for the 24-pin ATX connector and 4+4-pin CPU connectors with modular cables for drives, graphics cards, and peripherals. In some cases, higher-capacity pins help minimize voltage loss on modular designs. Being able to add or remove the peripheral cables as needed significantly improves your ability to manage cables.
Cable length is something you may want to consider, as well. Most modern PC enclosures that feature a PSU bay at the top or bottom of the case will accommodate cables in the 20-inch range (for the ATX 24-pin connector). When we have run into cable length issues, it has almost always been the 4+4-pin CPU power connector that just wasn’t long enough to make the journey behind the motherboard tray in a bottom-mounted PSU system. We love it when we encounter this problem, only to find the appropriate extenders right in the box. Longer cables will generally give you better cable management options, but when paired with a case with very little room behind the motherboard tray, this benefit can quickly become a nightmare, especially when it comes time to put that side panel back where it belongs.
Be Warranty Aware
In a perfect world, you could disassemble any power supply you planned to purchase and easily determine if the internal components, structure, and design met your personal quality standards. Sadly, opening up a PSU will almost certainly void the warranty (and can also be very dangerous). But there’s actually an easy way to figure out if the components in there are high quality. Just look at the warranty period. Although it’s not always the case, Japanese capacitors that are rated for 85 Celsius rank below those rated for 105 Celsius. PSUs equipped with the former will tend to have up to 3-year warranties, and the latter will tend to have 5- to 7-year warranties.
Another clue comes from the continuous power rating. If it is designed to run at continuous power at room temperature, expect a shorter life span, while 50 Celsius, as we mentioned earlier, is a server-grade environment. The PSUs certified to operate under such exacting conditions will tend to be better made and last longer.
Fans are also a mark or quality. Sleevebearing fans are common on entry-level PSUs, whereas ball-bearing and fluid dynamic-bearing fans, which operate longer and quieter, will tend to deliver more reliable performance.
Protective circuits have become fairly standard in the industry, but it’s always good to make sure the device you choose supports overvoltage, undervoltage, overcurrent, and short circuit protection. Current PSUs also feature integrated circuits that deliver better acoustics by letting fan speeds adjust to meet cooling demands.
Every PSU A Snowflake
PSUs are not like trucker hats, one size does not fit all. Targeting a PSU that can meet your component power demands regardless of how hard you push the system is the best way to keep it cool, quiet, and reliable.