How To Choose The Right Power Supply

Computers are typically built focusing on either processing speed or gaming performance as top priority. Components such RAM, motherboard, and even case tend to take a backburner position in the budget. Unfortunately, a lot of builders often relegate the computer’s Power Supply Unit (PSU) to an afterthought that gets the remnants of the remaining budget, or they get something that’s a large wattage number for the cheapest price. However, picking the right PSU is a more intricate and very important decision in a build. We’re going to go over things to consider so you can make an informed decision and pick the best power supply that’s right for you.

The TL;DR of it is find, at minimum, a Gold-rated PSU with a good warranty and is the right wattage for your needs. If you’re just looking to get by or on a really tight budget, a well-researched Bronze option can serve you for several years. Read on to find out why.

The Rating Game – Efficiency At A Glance

Back in 2004, Ecos Consulting launched a certification/branding program called “80 PLUS” that certifies the efficiency of power supplies. Knowing how efficient a PSU is helps you know how much extra power your components will end up pulling and how much power will be directly converted into heat before it even reaches your components. The 80 PLUS branding helps you recognize the efficiency at a glance so you can more-readily make a decision about a PSU, especially if it’s lacking third-party reviews with extensive testing.

The equation for calculating efficiency is rather simple: system component power divided by efficency percentage equals wall-power draw. For example: 300W system / 80% = 375W at the wall. That same system with a 70% efficient PSU was draw 428W, 53W more, just with a less-efficient PSU.

Now that we know how to calculate efficiency, let’s look at the efficiency ratings of the different 80 PLUS labels:

% of
Rated
Load
(@115V)
10%N/AN/AN/AN/AN/A90%
20%80%82%85%87%90%92%
50%80%85%88%90%92%94%
100%80%82%85%87%89%90%
% of
Rated
Load
(@230V EU)
10%N/AN/AN/AN/AN/A90%
20%82%85%87%90%92%94%
50%85%88%90%92%94%96%
100%82%85%87%89%90%94%
Image Source: Toms Hardware

As you can see, they’re trying to make the efficiency curve peak right around the 50% load mark. You can see this play out on the efficiency graph of a platinum-rated SeaSonic SSR-650PX (right) as tested by Toms Hardware. The PSU rises sharply to hit the target 90% efficiency at 20% (130W) load, but actually cresting just before 50% before tapering off. Our second table corresponds to the black line, showing the efficiency ratings on 230V power, common outside of the USA, particularly in the EU.

More Watts Is Better, Right? Nope.

If you’re building “the Ultimate Gaming Rig” like our own Enthusiast Build, you’d think snapping up a 1200W PSU would be the no-brainer option, but under extreme loads, the system would only consume (theortically) 495W and more typically 400W on average. If we look at the efficiency curve, the best place to target will be right around that 50% mark, with enough leeway to fall 10-20% to either side and still be fairly ideal, depending on budgeting or forethought for future upgrades (adding more drives, add-in cards, larger GPU, etc).

When would it be appropriate to pick something outside of this ideal range? You could select a fairly overpowered PSU because you wanted to take advantage of a silent-running option where the fan won’t spin until you hit a certain wattage/heat threshold if you’re looking to make a silent build. This would also be appropriate if you plan on running dual-GPUs in the future. Under-speccing your PSU is a little more risky. While PSUs are rated to provide their full load, running the components at the max rated power for long periods of time can cause undue wear, compared to running at a better 50% load. If you’re looking at skimping on wattage, hopefully your not also skimping on rating or looking in bargain basement brands with what little budget money you have left. We’ll discuss the nuance of ripple and noise further down, but suffice it to say, cheap PSUs can have the potential to damage internal components by ranging voltages out-of-spec or even be a fire hazard by cheaply implementing critical safety features, if including them at all. Fortunately, the more-common thing is they usually just shut themselves down well before their (over)rated sticker wattage. If you see a “700W” PSU with 2 SATA connectors, the motherboard connectors and a single six-pin PCIe plug and some molex connectors, you can be pretty sure that power supply won’t handle 700W. This happens a lot in the off-brand, sub-$30 range.

How To Tally Watts

Calculating system power can be as simple or complex as you’d like. If you want to do a (very) rough (usually over) estimate, here’s a simple chart to tally with:

ComponentWattsExampleWatts
CPUUse box TDP +20%3900X105W+21W
GPUUse box TDP (add 25% if any OC)Vega56190W+48W
Motherboard+RAM50W (this is our slush wattage)X570 Aorus50W
Drives10W/eaSamsung 860 Evo10W
WD 3TB Green10W
Total Estimate: 434W

If we look at the actual full-load rating of the CPU (142W), GPU (257W), Motherboard (<50W w/RAM), SSD (4W), and HDD (7W) power, you’ll see the end total estimated power of 434W is not far off the measured 460W power usage. This would make the Seasonic FOCUS Plus 850 Platinum that we recommended in our Enthusiast Build a solid choice for this example build.

What if you want to be more precise, or have additional components? Most PSU makers provide a wattage calculator on their website that might get a more-accurate calculation:

Seasonic Wattage Calculator
be quiet! PSU calculator
MSI Power Supply Calculator
OuterVision Power Supply Calculator

Fill one of those out, especially the OuterVision one, and you’ll see why rough estimates, though somewhat inaccurate, do well enough for the trouble.

Now I Know My Watts, Is The Price of Gold Worth It?

Now we know what our PSU wattage should be, what do we buy? Fortunately in the 850W range there’s not the sea of cheap terrible choices we see down in the more-common 400W range. However, if we stroll over to NewEgg and show 850W PSUs and order by price decending, we quickly come across several terrible options. An over-specced KenTek that doesn’t even have enough connectors to pull 400W, let alone the “850W” it’s claiming to be rated for, but still asking $60! An A-Power “800W” with only a single 6+2 PCIe connector for $69.

Things start to look up at $85 with an Enermax ETL800EWT-M that at least has enough PCIe connectors to actually potentially reach the rated 800W. The only review I could find, however, was for it’s 650W smaller sibling which did an entry-level job in the light testing it was put through. It matched the 80 PLUS Bronze specifications it’s labeled with. Being full of the cheaper capacitor variants will certainly limit the lifespan of the PSU though, which shows in a 3-year warranty.

Skipping forward to a good brand option in the Gold level is a PC Power & Cooling ZX 850W at $109 which reviewed pretty well, using quality Japanese capacitors rated for higher temperatures than cheaper PSUs use and other branded components. There’s several circuitry protections for over-current, over-voltage, and short-circuits that are either insufficiently short-cutted or skipped altogether in cheap PSUs. At least the quality of the unit merits a bump to a 5-year warranty. EVGA offers Gold-rated PSUs with up to a 10-year warranty as well for $120 (only $11 more).

In running contention with our previously-recommended Seasonic at the Platinum level, the EVGA 850W PQ at $154 and Corsair HX850 Platinum at $165 keep it in good company, offering loads of premium features similar to some quality Gold units, but with the extra bit of circuitry and component quality to bump the efficiency to Platinum levels.

There’s a fairly obvious line drawn at the Gold rating where internal components switch over from low and mid-grade Taiwanese and Chinese brands to the higher-grade Japanese components. Combined with better performance in keeping voltage fluctuation (ripple) to a minimum and reducing or eliminating induced current or voltage (noise), makes Gold, in my opinion, an ideal inflection point in performance and quality vs price.

You can also look up your desired power supply and see which OEM made the design at this PSU database. You’ll see a small set of OEMs are usually rebranded by other more-recognized names, so you can see if two competing PSUs are actually designed by a more-preferred OEM.

Cost By The Numbers

Let’s run through some math to determine the difference between a cheaper Bronze unit and a more expensive Gold or even Platinum option. We’ll assume a flat $0.10/kWh, as not everyone has cheap hydro power and just to make the math cleaner. We’ll base this in the USA, since it has the worse-efficiency 115V curve (and we’re using $USD anyway). We’ll also assume an Enthusiast level of use, gaming for 5 hours a day on a 425W rig (since we have the minimum efficiency specification for each tier at 50% load), and doing minor 170W (20% load) browsing, email, etc for another 2 hours. We’ll assume the machine is turned off when not in use and we actually go outside on the weekends instead of playing Fortnite and PUBG (yes, this is likely where we stray from reality, I know, but hear me out), so we do this workload for 5 days a week over a full year.

Here’s a quick example of the math that I’ll then fill out the table below with results:
(( 425W / 0.80 * 5hrs ) + ( 170W / 0.80 * 2hrs )) / 1000W = 3.08125 Daily kWh * 5 days = 15.40625 Weekly kWh * 52 wks/yr = 801.125 kWh/yr * $0.10/kWh = $80.11/yr

PSU RatingEff @20%/50%Daily kWhWeekly kWhAnnual kWhAnnual Cost
80 PLUS80%/80%3.0812515.40625801.125$80.11
80 PLUS Bronze82%/85%2.9914614.95732777.7805$77.78
80 PLUS Gold87%/90%2.8203114.10153733.2797$73.33
80 PLUS Platinum90%/92%2.7306713.65338709.9758$71.00

Obviously, the power usage and efficiency numbers don’t make a huge difference with someone that games 25hrs a week and surfs for another 10hrs, having just a $9 spread for one year of use. It matters even less for a lower-power computer as well. But there’s a reason I brought in component quality and warranties. PSUs can, and do, die. I’ve seen dying PSUs cause system instability (gremlins like BSODs and USB malfunctions to full power-off events). I’ve had a PSU kill a motherboard when it died. Fortunately, most of the dead PSUs I’ve dealt with have been just the silent death of only-lights-up-the-motherboard-but-won’t-boot type. They can happen to any quality of PSU, but I can assure you they’ll happen more frequently on the lower-grade PSUs. Let’s assume the unlikely event that each PSU in our 4 tiers dies at least once. Once for the Gold and Platinum tiers, and twice for the base PLUS and Bronze (outside of warranty of course, since the warranties are so short for these two tiers), just to make things fair and somewhat representative of quality. Now, a new chart for our 10-year costs:

PSU RatingPSU CostWarrantyReplacement Costs10-year Power CostTotal Cost over 10 years
80 PLUS$591yr$118 (likely more)$801.10$978.10
80 PLUS Bronze$853yr$170$777.80$1032.80
80 PLUS Gold$12010yr$0 (replaced under warranty)$733.30$853.30
80 PLUS Platinum$15910yr$0 (replaced under warranty)$710.00$869.00

Obviously only replacing twice the best stand-in for an 80 PLUS I could find in the 850W range is a rather optimistic understatement, a Bronze PSU lasting at least 4 years before dying is more reasonable. Fortunately for the Gold and Platinum tiers, even if they did die, they’d be under warranty in this 10 year window we’re looking at. So the real hidden costs is the replacement of dead PSUs and any components that went with it. I’m not going to scare you with burned-out PCs and house fires as they’re very rare, but dead motherboards from a PSU failure aren’t as uncommon.

Conclusion

The power efficiencies of each tier really aren’t an important of a factor unless your running a rendering server or similar high power draw nearly continuously every day of the year. A gamer scenario has only a $6.70 spread between a Bronze and a Platinum over a 1-year period. The quality (and consequentially longevity) of internal components, a lengthy warranty, and quality-of-life features like silent running at low power, and advanced circuitry features for more-stable internal power delivery will be the reasons to lean towards Gold and notably Platinum tiers. Not having a system outage, or worse yet, data or component loss, due to a failed PSU is well worth spending up to the most reliable PSU you can get, which is most likely to be the highest tiers.

You’ll note I never really focused on other quality-of-life features such as modular cables, RGB, or coil whine/fan noise. Frankly, they’re niceties that really help certain builds for display or cable management. Coil whine and fan noise are virtually nonexistent in the premium Gold and Platinum tiers and can be an RMA-able offense (for coil whine at least). You should always read a well-detailed review of your desired power supply. It will likely be with you for ten years or more, so choose well-informed and wisely.

Also, capacitors can wear out over time and become less efficient. It may be well-advised to consider proactively replacing your power supply prior to it actually failing. After ten years of trouble-free running, it’s likely made up for your investment several times over.

As a last pro-tip: always use a certified surge protector with a high joule rating to protect your electronic equipment. Better yet, you could use a line-interactive UPS to provide clean, filtered power to your computer and keep your system running during brief power upsets. This will help ensure the longevity of your new power supply.

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