Corsair RM850x (2021) Power Supply Review

The Corsair RM850x is the new leader in the 850W Gold category.

Corsair RM850x (2021)
(Image: © Tom's Hardware)

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It can't be easy to upgrade a platform that was already among the best in the Gold efficiency category, but Corsair managed to do it with CWT's help. The new Corsair RM850x achieves higher overall performance than its predecessor thanks to its amazing ripple suppression, tighter load regulation and higher efficiency, especially at light loads. The hold-up time is also longer, while inrush currents remain at the same low levels. The only sections where the old RM850x prevails are transient response at 3.3V, which is not of great importance, and noise output because of the more aggressive fan speed profile and the new ML fan of the new unit. Despite the increased overall noise output, we still prefer the new ML fan because it is super reliable even under high operating temperatures. 

(Image credit: Tom's Hardware)

The competition in the 850W Gold efficiency category is fierce but the new Corsair RM850x achieves first place in our overall performance chart, with the Super Flower Leadex III unit following. The latter has been replaced by the Leadex V model, which we haven't received yet, for review. Other notable mentions in this category are the XPG Core Reactor 850W, the Cooler Master V850 Gold V2, and the Corsair RM850 which has a lower price tag than the RM850x. 

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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.

Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.

  • Isokolon
    shame they changed the fan. the 2015 & 2018 RMx were so great for low-noise enthusiasts.
    how the review classifies an almost 30db unit as "quiet" is beyond me.
    Reply
  • Udyr
    What makes this unit better than the Toughpower GF1?

    https://www.tomshardware.com/reviews/thermaltake-toughpower-gf1-850w-power-supply
    Reply
  • g-unit1111
    I have an RM750x and it is a really great PSU. You can't go wrong with this unit.
    Reply
  • jsz031
    Hi Aris.. like your reviews..

    small question. I noticed the Bulk/hold up caps get higher with wattage. can you explain how this impacts a general PSU?

    for example/off topic, I have a 5 year old 550w G2 and it has a 400v 470uf cap. Just purchased a 550w g3 and the cap is lower capacity @ 400v 390uf.

    Does this mean anything or am I overthinking it? is the 550w g2 better than "base" spec? I understand leakage can occur over time, I'm just not sure if its a downgrade or upgrade in specific areas.

    thank you.
    Reply
  • jayjr1105
    jsz031 said:
    Hi Aris.. like your reviews..

    small question. I noticed the Bulk/hold up caps get higher with wattage. can you explain how this impacts a general PSU?

    for example/off topic, I have a 5 year old 550w G2 and it has a 400v 470uf cap. Just purchased a 550w g3 and the cap is lower capacity @ 400v 390uf.

    Does this mean anything or am I overthinking it? is the 550w g2 better than "base" spec? I understand leakage can occur over time, I'm just not sure if its a downgrade or upgrade in specific areas.

    thank you.
    As long as they are meeting the ATX spec of 17ms hold up time, it doesn't really matter. The G2 was probably overkill so they cut costs by going with a lower capacity one.
    Reply
  • tomkawal
    Admin said:
    The new Corsair RM850x is among the best PSUs in its category.

    Corsair RM850x (2021) Power Supply Review : Read more
    ..and worst quality coming from production line! Mine was covered with thick layer of metal salts from soldering. It stopped turning on. Works again after thorough cleanup.
    Reply
  • tomkawal
    Beautifully presented. I was not so lucky with the unit I got, which stopped working after a month. Sent back to eBuyer guys and received it again not fixed (generally they requested ALL cables where I wanted only brick swap - this is totally unacceptable for me when the wires are in place tied to enclosure!) Raised ticket with Corsair with no answer in 2 days. Fixed on my own with one hour of cleaning the PCB from thick layer of soldering flux on the bottom side of PCB which caused leakage currents all over the board. Now it works. Horrendous experience and I don't recommend none of these businesses.
    Reply