Perhaps the most important thing to keep in mind is that because all switching PSUs have been designed so as to deliver their maximum efficiency at about half-load – about 50% of their rated maximum capacity – that the efficiency of a PSU at any given moment is strongly tied to the load on that PSU. A PSU’s performance will drop not only at higher loads but at lower loads as well, and this is especially the case at the low-end of the curve – usually below 15% of the unit’s rated capacity – where efficiency outright plummets. Meanwhile you should keep in mind that the advertised performance of a PSU is within the nominal load range (20% to 100% of its rated capacity) and the manufacturer is not obliged to include information on how much the performance degrades at sub-20% load conditions. As a result, the selection of a severely oversized PSU can be very counterproductive if a system spends most of its time operating in that inefficient area below 20%.
That being said, the selection of a PSU is based on both objective (e.g. wattage, performance) and subjective (e.g. design, modular cables) parameters. Consequently, picking a proper PSU requires making a bit of an educated guess about the power requirements of the system, and this process often results in builders greatly overrating the power requirements of their systems. It is not uncommon for people – even store salespersons and experienced builders – to recommend a 1kW unit to a user with just two (or even one) high performance GPUs. Meanwhile “wattage calculators,” though an improvement from blindly guessing, are usually simple tools that get their numbers from the design power (TDP) specifications of components. The TDP of a component does not represent the actual power requirements of a component – it’s at best a broad guideline – and it also is next to impossible to place every single component of a system under maximum stress simultaneously. A system with a single CPU and a single GPU rarely requires more than 300 Watts.
If you are able to measure the actual power requirements of your system, the best thing to keep in mind that you should not buy a unit that will frequently operate near its maximum capacity. Just as you would not run your car constantly near the red line, a PSU should not be under maximum stress for prolonged periods. A high quality PSU can withstand it, but just because it can does not mean it should. Again, all switching PSUs deliver their maximum efficiency at roughly 50% of their rated capacity. Running a PSU at over 90% capacity for prolonged periods of time will not only reduce its performance but it will also make it hotter, louder, and decrease its expected lifespan.
With that in mind, while the recommendations of the online tools and calculators may be overestimated, they’re not overly so. Selecting a PSU near the capacity they recommend is not usually a bad idea, as the recommendation usually is twice the actual power requirements of the system. The common mistake is that users usually seek to buy a significantly more powerful unit, thinking that having extra power helps, and end up with a severely oversized PSU for their system that will be both more expensive to purchase and unable to perform as it should.
Finally, getting to our recommendations, for easier reading we will split our recommendations into five main wattage categories with at least two units for each. One selection will be based on the maximum possible value (e.g. bang for the buck) and one will focus on the best overall performance.
300 to 400 Watts: Antec EarthWatts EA-380D & Sparkle R-FSP400-60ETN
Although these power ratings probably appear too low to advanced users, such a PSU is more than enough to power a modern low energy PC with a mainstream CPU and GPU, plus a couple of drives. Our recommendation to those aiming for the lowest possible price for a product of acceptable quality remains unchanged since last year and is the old but proven Antec EarthWatts EA-380D. This design is now over five years old but it remains a solid performer and retails for just $29 after rebate.
For those seeking higher performance and are willing to pay something extra for it, Seasonic’s SSR-360GP 80Plus Gold certified offering retails for $60 including shipping and comes with a 5-year warranty. However, Sparkle’s R-FSP400-60ETN 400W PSU retails for $64 including shipping and is an 80Plus Platinum certified design. Sparkle’s offering is based on a FSP platform, a reputable OEM but not as loved as Seasonic. We do recommend the slightly higher efficiency of the R-FSP400-60ETN, but the SSR-360GP remains an excellent alternative.
400 to 600 Watts: Corsair CS450M & Seasonic SS-520FL2
This is the power range with the largest selection of products and for a good reason, as it generates the largest portion of sales. It is extremely unlikely that a PC with a single CPU and a single GPU will overcome the output of such a PSU, even if overclocked.
For those seeking to combine good performance with reliability and value, Corsair’s CS450M is currently retailing for $50 after rebate. It would be difficult to find another 80Plus Gold certified and modular PSU for that price but Cyonic’s AU-450X is a good alternative with higher overall performance at $70 after rebate.
600 to 800 Watts: XFX TS P1-650G-TS3X & Corsair HX750i
PSUs with an output between 600 and 800 Watts are very popular amongst gamers and overclockers. They are powerful enough for dual GPU gaming systems and provide enough overhead for serious overclocking and mods. This power band is also popular among users that will be using just one GPU, as the power overhead frequently creates a feeling of security.
For those seeking to combine performance with value, the XFX TS P1-650G-TS3X is quite a deal. It is based on a Seasonic platform, is 80Plus Gold certified and comes with a 5-year parts & labor warranty, all for just $60 after rebate. If you are looking for an alternative, or if you are looking for a modular design, the units of Corsair’s new RMx series is quite a good deal as well, retailing at $70 after rebate for the 650W version and $80 after rebate for the 750W version.
If you are looking for high performance within this power band, our recommendation would be the Corsair HX750i. It is a modular 80Plus Platinum certified PSU, covered by a 7-year warranty and features Corsair’s Link interface. We found it retailing for $140, a reasonable price considering its quality, features and performance. Another very high quality alternative would be the Seasonic SS-760XP2, an outstanding PSU that is overshadowed by its exceedingly steep price. The Seasonic SS-760XP2 currently retails for $160. Although we cannot easily justify the higher price over the HX750i, it is an exceptional product and could be a viable alternative if the price gap between the two products narrows or if the HX750i is unavailable.
For those with high end dual-GPU or triple-GPU computers, a PSU with an output between 800 and 1100 Watts is essential. Whether it is a gaming or a professional system, a good power supply is required for its reliable operation. To that end, our primary recommendation would be Corsair’s RMx series, as they combine good quality, performance and efficiency. The 80Plus Gold certified RM850X and RM1000X retail for $85 after rebate and $120 after rebate respectively, a very fair price compared to the competition. Our secondary recommendation would be the EVGA SuperNOVA 1000 G2, a PSU that we tested and found to have excellent electrical performance and quality, but the retail price increases to $150.
When performance is a greater concern than value, then Seasonic’s SS-1050XP3 is our primary recommendation. The modular 80Plus Platinum certified PSU brings impressive performance and quality to those capable of affording the steep $210 price tag. Another good alternative would be the EVGA SuperNova 1000 P2, a PSU based on SuperFlower’s Leadex platform. It has virtually the same features as the SS-1050XP3 and retails for $200 including shipping. Both PSUs appear equally good on paper but our primary recommendation is the SS-1050XP3, as we have hands-on experience on its exceptional power output quality and performance.
If you require a PSU with this kind of output, chances are that you have at least three high-end GPUs and or a seriously powerful dual-CPU system with a lot of devices. These PSUs also find use in advanced servers and cryptocurrency mining systems. That being said, the PSU is going to be powering a rather expensive system, the function of which is frequently very important. Therefore, the selection of a “value” PSU within this power band is a complex procedure as it has meet very high reliability standards. With that in mind, our recommendation goes to the Seasonic SS-1200XP3, a very reliable 80Plus Platinum PSU that retails for $210 after rebate. It is not the cheapest 1200W PSU available but it offers a very good combination of value, performance and quality. Corsair’s AX1200i is an interesting alternative as well, mainly for the Corsair Link interface feature and its excellent performance, but the retail price increases to $300.
For those that want the absolute best and cost is not an issue, Corsair’s AX1500i remains the undisputed champion. It is one of the very few 80Plus Titanium certified units available, has exceptional overall performance and outstanding quality. There is virtually no other PSU available today that combines the quality, performance, efficiency and features of the AX1500i. The only problem is that the AX1500i currently retails for $410, enough money to buy a complete mainstream system.