The new RM850x and RM750x PSUs are noticeably smaller than their predecessors, while overall performance is about the same and noise output is even lower. Corsair was clearly going for a slight evolution here, and we observed a number of component changes inside the RM850x V2, including different controllers on the primary and secondary sides, that enable this. Moreover, a PIC microcontroller inside the RMx V2 PSUs is used to control the fan's operation, enabling slower rotational speeds and more conservative acoustics.
Overall, the RM850x V2 is a fine PSU registering tight load regulation, great ripple suppression, good transient response, and quiet operation, even under tough operating conditions. In fact, this is one of the quietest 850W PSUs that we have tested.
Despite the internal changes, Corsair left the RM850x's enclosure alone. This isn't necessarily a problem, since PSUs mostly spend their time hidden in your chassis. But it'd be nice to see Corsair update the external design to match its improvements elsewhere. That'd clearly distinguish the new RMx PSUs from the old ones (though it seems like Corsair specifically doesn't want to, given identical naming).
We're pretty sure that Corsair's most popular power supply family is the RMx, and we wouldn't be surprised if that remains the case moving forward thanks to CWT's upgraded platform. Although the RMi family, which gives you compatibility with Corsair Link software and a FDB fan, isn't much more expensive, enthusiasts in this price range often prioritize saving a few dollars over a handful of extra features.
Thus, the RM850x V2's most prominent competition comes from EVGA's 850 G3 and Seasonic's Focus Plus Gold 850W. The 850W Aerocool Project 7 is also a good alternative. But none of those PSUs are able to beat the RM850x V2 when it comes to noise output. This CWT platform is as quiet as it gets for an actively-cooled 850W PSU. Only the Aerocool ACP-850FP7 achieves a similar Cybenetics noise rating (LAMBDA-A+, 15-30 dB[A]). EVGA's 850 G3 and Seasonic's SSR-850FX are notably noisier, earning LAMBDA-S++ (30-35 dB[A]) ratings. So, if you want a great-performing and ultra-quiet PSU that's also backed by a 10-year warranty, the RM850x V2 is an excellent choice. The 750W and 850W competition is brutal, but Corsair has powerful contenders of its own. It's one of the few companies that takes acoustics seriously, giving it a big advantage when noise matters.
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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, Purch Media, are financially involved with Cybenetics. Aris does not perform the actual certifications for Cybenetics.