Building three PCs: Power formalities

Article By : Brian Dipert

Picking the optimum power supply for your PC "build" is a critical decision to ensure assembled-system operational success and long operating life.

Now that I’ve caught you up on the CPU, core logic, motherboard, memory and other minutia of the third computer I plan to soon start building, it’s time to wrap up this PC building-block blog post series with details on two final important hardware subsystems for all three PCs:

  • Power supplies (PSUs) (for “intake”), which I’ll discuss today, and
  • Heat-removing techniques (to handle excess “outflow”), a topic which I’ll cover in a separate post to follow this one in short order

Regarding PSUs, let’s first review the 80 PLUS certification program and its various certification levels. As Wikipedia describes it:

80 Plus (trademarked 80 PLUS) is a voluntary certification program launched in 2004, intended to promote efficient energy use in computer power supply units (PSUs). Certification is acquirable for products that have more than 80% energy efficiency at 20%, 50% and 100% of rated load, and a power factor of 0.9 or greater at 100% load.

And what’s power factor, again? Glad you asked; here’s Wikipedia again:

The power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit…A power factor of less than one indicates the voltage and current are not in phase, reducing the average product of the two. Real power is the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of RMS current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power.

Regarding the various 80 PLUS certification levels, Tom’s Hardware has a solid writeup on the topic; I’ll summarize them in the following table:

That a particular manufacturer has pursued 80 PLUS certification isn’t guaranteed with any particular PSU; you may have noticed, for example, that the power supplies I put in the two systems I built and subsequently donated didn’t document their certification status at all. That said, my overall market analysis matches Tom’s Hardware’s perspective: “Most manufacturers prefer to flog either the Bronze (budget-minded) or Gold (premium-minded) levels.”

Long-time readers may already suspect that I “bleed green” (i.e., I’m an avid environmentalist), and therefore are not surprised to read that all of the PSUs I picked for the systems I’ll be building for my and my wife’s regular use are 80 PLUS Gold-certified at a minimum (Tom’s Hardware’s perspective: “usually the best efficiency-per-dollar score is delivered by Gold units”). One of them, as you’ll soon see, is even 80 PLUS Platinum (Tom’s Hardware: “The prices of Platinum-certified PSUs fell significantly once Titanium units made their appearance.”).

Power supplies come in various form factors, as well as various size dimensions within each form factor standard; unsurprisingly, the more compact and/or less common the variant, all other factors being equal, the more expensive it tends to be. The enclosures I used for all three systems I’m building, even the two compact mini-ITX-based ones, can handle a standard ATX (also known as PS/2) power supply, versus a smaller CFX, SFX, or TFX unit.

You’ll need to make sure that whatever PSU you choose has enough, and the correct, outputs to drive whatever components require power; the motherboard, CPU, fan(s), graphics and other PCI Express cards, and various mass storage devices (HDDs, SSDs, optical drives, etc.), for example. Fortunately, adapters exist to convert from one connector standard to another, as well as to split one output into multiple outputs (if you need to drive multiple system fans, for example). Be careful using a splitter to subdivide one PSU output into multiple connectors, however, since you’re still fundamentally limited by the maximum current output of each PSU voltage “rail.”

More generally, speaking of maximum power output, make sure that the PSU you choose can supply enough current (at stable output voltages!) to adequately fuel all components in your system. Keep in mind that the thermal design power (TDP) spec for a CPU may undershoot its peak power draw in “turbo” operating modes. And you might also want to build some “padding” into the design to account for future upgrades to higher-power consuming graphics cards, for example.

Another reason to pick a higher-power PSU than your arithmetic would otherwise suggest is that PSUs tend to run most efficiently at ~50% of full rated load; you may have already ascertained this from the 80 PLUS certification level table earlier in this writeup. High efficiency not only translates into less input power waste, it also translates to cooler operation, which leads to longer operating life. Fortunately, various PSU Calculators (such as this one from Newegg) exist to assist you in picking a sufficiently powerful PSU for your particular build.

So after this lengthy and educational (hopefully!) “setup,” which PSUs did I choose for my three systems? The AMD CPU-based mini-ITX one is the lowest power-consuming of the bunch, thanks both to its energy-thrifty microprocessor and its modest graphics card. A ~500W PSU should be plenty, I determined, and I initially planned to go with a Corsair CX500 that I’d bought several years earlier on sale for $37.99 from Newegg and still had sitting around unopened.

It was an 80 PLUS Bronze unit (which I’d at the time acquired then-unenlightened as to the certification level differences), however, which gave me pause for already-stated “green” reasons. Plus, it’s a non-modular unit (although the “stock” photo above doesn’t make this clear), a term that begs for a bit more education explanation: Non-modular PSUs include ALL voltage output cabling and connectors already attached to the PSU, regardless of whether your particular “build” will need all of them. At minimum, the non-modular implementation is non-aesthetic; you end up with a bundle of wires and plugs that you need to stow away somewhere. And in a diminutive mini-ITX enclosure like the one I’m using, a non-modular PSU might be a flat-out non-starter due to insufficient available room in the enclosure or, at minimum, egregious airflow impacts caused by the bulky cable-and-connector bundle.

Semi-modular PSUs, as their name implies (versus the sometimes instead used, and deceptively so, alternative “modular” qualifier), direct-attach only the cabling that all systems require: the motherboard, system fan and CPU power feeds, for example. All other power outputs (for SATA storage devices, say, or PCI Express add-in cards) are handled by a set of wiring harnesses that attach to multiple connectors on the side of the PSU, any (or all) selectively utilized as needed. And full modular PSUs take the implementation to the opposite end of the spectrum: there are no output power wires coming directly out of the PSU, only connectors that mate with harnesses. Unsurprisingly, non-modular PSUs tend to be the least expensive, all other factors being equal, with fully modular PSUs the priciest.

Instead of the Corsair CX500, therefore, I ended up going with EVGA’s SuperNOVA 550 GA, a 550W fully modular 80 PLUS Gold PSU, which I’d found in late April for $64.99 at Amazon (it’s now $49.99 at Amazon as I write this, however…sigh…):

The above photos show the unit complete with the aforementioned modular connectors, along with the various optional wiring harnesses.

The Intel CPU-based mini-ITX system was a bit more power hungry, due both to its notably more current-demanding CPU and its somewhat more demanding GPU. Here I went with another fully modular 80 PLUS Gold PSU from EVGA, this the 650W SuperNOVA 650 GT, which I’d purchased last December for $79.99 after $10 rebate at Newegg (where it’s currently $69.99 with no rebate requirement…sigh redux):

And finally for the AMD-based ATX system, I originally was going to use a 700W 80 PLUS Gold PSU, Rosewill’s LEPTON 700, which I’d also purchased last December from Newegg for $79.99 (Rosewill is Newegg’s “house” brand, although some Rosewill products are also available for purchase at Amazon and other retailers):

It’s semi-modular, which didn’t concern me, as there’s plenty of room in the ATX case for the cabling. What did concern me post-acquisition, however, is the seemingly spotty reliability record reflected in the user feedback now posted to Newegg’s website. That Newegg no longer sells this particular model is doubly disconcerting. So, although (as with the Corsair CX500) I’ll likely hold onto it as a spare, I instead went elsewhere for this system’s primary PSU. Specifically, I’ve selected a 750W 80 PLUS Platinum unit, SeaSonic’s PX-750, which in late May Newegg was selling for $114.99 after $20 rebate:

I admittedly paid a bit more than I might have for a 750W PSU elsewhere (although less than I normally would…the PX-750 is currently selling for $149.99 at Newegg as I write this), but SeaSonic has a pretty pristine industry reputation, and the 80 PLUS Platinum certification was a plus. And if you’re wondering why I got such a beefy PSU, given that this particular system is based on a low-power AMD CPU and the planned graphics card is also modest in its energy demands, I made my choice with an eye toward potential future graphics enhancements. Specifically, deep learning model training would demand a more modern and “beefy” GPU, and higher-end content creation applications would also benefit from the graphics upgrade.

Speaking of reputations, and of reliability, I’ll close with a recommendation. No matter the manufacturer or model of PSU you’re considering, you’ll undoubtedly encounter single- (or no-) star reviews on it from disgruntled owners. Often the PSU itself isn’t at the root of the issue; perhaps a component on the motherboard or peripheral connected to the PSU has failed, for example, or the system’s enclosure (or environment) is insufficiently ventilated, resulting in overheating-induced accelerated failure. Or maybe the consumer has just over-economized by selecting a PSU that’s insufficiently powerful for the system’s peak power demands; whenever you read that someone’s system has abruptly shut down in the middle of a demanding gaming or rendering session, this particular root cause is particularly likely.

But sometimes the PSU itself is to blame. Perhaps the manufacturer has cut corners on component selection or circuit design, to shave some cost. Or maybe the components themselves are to blame; many of you likely still remember the “bulging capacitors” debacle long documented in EDN by yours truly and others. Failure can sometimes lead to fireworks:



But often the symptoms aren’t quite as dramatic, although the dead-PSU result is the same…an outcome that may also result in the failure of other, even more expensive connected devices due to transient voltage and current spikes and the like. So what can you do to minimize the probability of failure, and/or to smooth the recovery process from a failure? Glad you asked:

  • Buy PSUs from only reputable manufacturers and purchase only robust models. Keep in mind, as I already said, that you’ll always find at least a few negative reviews (in no small part because folks who have had a bad experience are much more motivated to post a review than those whose experience was smooth). Statistics is your friend here. What’s the ratio of positive to negative reviews? And equally important, what’s the total number of reviews?
  • Use an online PSU Calculator (or your own calculator) to select a sufficiently powerful supply for your system’s peak power demands…and consider adding some “pad” for incomplete arithmetic and/or future potential upgrades.
  • Consider buying a supplemental warranty from SquareTrade (now owned by Allstate) or another reputable vendor, if offered by the retailer. I realize that PSUs often come standard with multi-year warranties. But getting the manufacturer to honor that warranty can be a tedious, time-consuming and otherwise frustrating process. SquareTrade/Allstate and its peers tend to be comparatively smooth and speedy, and the added cost is usually minimal.

I originally planned to cover both power supplies and thermal topics in one blog post, but seeing as I’ve just crossed through 2,000 words, I’ve apparently as-usual underestimated upfront my propensity for verbosity. I’ll therefore wrap up for now, with a promise to cover airflow architecture, liquid cooling, and the like in another post to come soon. Until then, I as-always welcome your questions and other thoughts in the comments!

This article was originally published on EDN.

Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.


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