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)

Why you can trust Tom's Hardware Our expert reviewers spend hours testing and comparing products and services so you can choose the best for you. Find out more about how we test.

Protection Features

Check out our PSUs 101 article to learn more about PSU protection features.

Swipe to scroll horizontally

OCP (Cold @ 25°C)

12V: 87.2A (123.16%), 11.879V
5V: 31.5A (157.5%), 4.946V
3.3V: 31.8A (159%), 3.276V
5VSB: 5.1A (170%), 4.977V

OCP (Hot @ 43°C)

12V: 87.4A (123.45%), 11.9V
5V: 31.5A (157.5%), 4.948V
3.3V: 31.7A (158.5%), 3.269V
5VSB: 5.1A (170%), 4.981V

OPP (Cold @ 28°C)

1049.07W (123.42%)

OPP (Hot @ 45°C)

1053.31W (123.92%)

OTP

✓ (140°C @ 12V Heat Sink)

SCP

12V to Earth: ✓
5V to Earth: ✓
3.3V to Earth: ✓
5VSB to Earth: ✓
-12V to Earth: ✓

PWR_OK

Proper operation

NLO

SIP

Surge: MOV
Inrush: NTC Thermistor & Bypass relay

Over power protection is adequately set, and the same goes for the OCP at 12V. On the contrary, OCP is highly set on the minor rails for no reason. Lastly, all other protection features are present and work well. 

DC Power Sequencing

According to Intel’s most recent Power Supply Design Guide (revision 1.4), the +12V and 5V outputs must be equal to or greater than the 3.3V rail at all times. Unfortunately, Intel doesn't mention why it is so important to always keep the 3.3V rail's voltage lower than the levels of the other two outputs.

The 3.3V rail is always lower than the other two, so there is no problem according to the ATX spec's requirements. 

Cross Load Tests

To generate the following charts, we set our loaders to auto mode through custom-made software before trying more than 25,000 possible load combinations with the +12V, 5V, and 3.3V rails. The deviations in each of the charts below are calculated by taking the nominal values of the rails (12V, 5V, and 3.3V) as point zero. The ambient temperature during testing was between 30 to 32 degrees Celsius (86 to 89.6 degrees Fahrenheit).

Load Regulation Charts

Efficiency Graph

(Image credit: Tom's Hardware)

Ripple Graphs

The lower the power supply's ripple, the more stable the system will be and less stress will also be applied to its components.

Infrared Images

We apply a half-load for 10 minutes with the PSU's top cover and cooling fan removed before taking photos with a modified FLIR E4 camera able to deliver an IR resolution of 320x240 (76,800 pixels).

The heat sinks on the board that hosts the 12V FETs are the hottest part, with the main transformer following. Still, the operating temperatures are kept low. 

MORE: Best Power Supplies

MORE: How We Test Power Supplies

MORE: All Power Supply Content

Aris Mpitziopoulos
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