Seasonic's Focus platforms are among the most popular around because they offer a solid list of capabilities for the price you pay. The SSR-650PX costs about $110, yet serves up tight load regulation, good ripple suppression, and of course high efficiency since it is 80 PLUS Platinum-certified.
The only weakness we identified was the minor rails' transient response, which lags the competition's performance. Those rails are referred to as minor for a reason: they aren't heavily used any more. Still, for as long as they're part of a power supply's specifications, we expect them to perform optimally. Apparently, more capacitance is needed in the corresponding regulation circuits to achieve smaller deviations during transient loads, increasing production cost. Of course, there is no perfect product. Although the SSR-650PX fares really well right out of the box, it'd be even better with a bit of tuning on the minor rails.
This is a highly capable PSU able to power potent gaming and video editing workstations. That's one reason we'd like to see Seasonic include a second EPS connector, which would make the SSR-650PX compatible with motherboards built for AMD's Threadripper CPUs. Currently, there are very few 650W PSUs with two EPS connectors (Aerocool's Project 7 650W and be quiet!'s Dark Power Pro 11 650W are two examples), and those cost more than Seasonic's offering. Nonetheless, we think high-efficiency models in this capacity range should be ready to support enthusiast-oriented platforms. Under normal (not overclocked) conditions, a solid 650W PSU can accommodate two fast graphics cards without a problem. So why limit the PSU's compatibility with a single EPS connector? On the other hand, you could argue that Seasonic's SSR-750PX sells for just $10 more, includes the two EPS cables we're asking for, and offers 100W-higher capacity.
There is no doubt that the 650W Focus Plus Platinum serves up significant value. This PSU is one of the best options in its capacity class. You only need to look elsewhere if the SSR-650PX's noise is an issue. Corsair's RM650x is one option, though it's less efficient, as is the Aerocool Project 7 650W, which costs more and can be difficult to find.
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Disclaimer: Aris Mpitziopoulos is Tom's Hardware's PSU reviewer. He is also the Chief Testing Engineer of Cybenetics, and developed the Cybenetics certification methodologies apart from his role on Tom's Hardware. Neither Tom's Hardware nor its parent company, Future PLC, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.