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)

Tom's Hardware Verdict

Corsair managed to improve the already great RM850x, offering even higher performance and a magnetic levitation fan.


  • +

    Full power at 47 degrees Celsius

  • +

    High overall performance

  • +

    Quiet operation

  • +

    Fully compliant with ATX v2.52

  • +

    Highly efficient at light loads

  • +

    Long hold-up time

  • +

    Low inrush currents

  • +

    Magnetic Levitation fan

  • +

    Loads of cables and connectors

  • +

    Fully modular

  • +

    10-year warranty


  • -

    High OCP triggering points on the minor rails

  • -

    Transient response at 3.3V could be better

  • -

    In-cable capacitors

  • -

    Small distance between peripheral connectors

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.

It is tough to upgrade something that's already quite good. But Corsair managed to do so with the RM850x power supply, improving the efficiency at light loads, adding one more EPS connector, and using a top-notch magnetic levitation fan. This is a product worthy of our list of the best power supplies. Its competitors include the XPG Core Reactor 850W and the similar capacity Cooler Master V850 Gold V2 model. The more affordable Corsair RM850, which is close in performance to the RM850x, is another fine option in this category.  

Corsair's RMx line is among the most popular in today's mid-segment PSU market, so updating was a daunting task.

The use of a magnetic levitation fan is a great asset. The rifle bearing used in the previous generation RMx line was good, but there is no comparison with the ML fan that the new units utilize; Rifle and fluid dynamic bearings cannot cope with high operating temperatures. The only problem is the more aggressive fan profile, but updates from Corsair mean the new RM850x batches have lower average noise output than the initial production units. 

The RM850x (2021) is the strongest member of the line, with enough power to handle a strong gaming system or a video editing workstation. To support the ultra-high-end mainboard, Corsair equipped it with three EPS connectors, something that's hard to find in today's market, even in stronger PSUs. The fully modular cable design is a must in this price range, and the same goes for the ten-year warranty, from the moment all competing offerings are supported by equally long warranty periods. Lastly, the PSU's dimensions are normal with 160mm length, so there won't be any compatibility issues with ATX cases. 


Swipe to scroll horizontally

Manufacturer (OEM)


Max. DC Output



80 PLUS Gold, Cybenetics Gold (87-89%)


Cybenetics A- (25-30 dB[A])


✓ (Fully)

Intel C6/C7 Power State Support

Operating Temperature (Continuous Full Load)

0 - 50°C

Over Voltage Protection

Under Voltage Protection

Over Power Protection

Over Current (+12V) Protection

Over Temperature Protection

Short Circuit Protection

Surge Protection

Inrush Current Protection

Fan Failure Protection

No Load Operation


140mm Magnetic Levitation Fan (NR140ML)

Semi-Passive Operation

Dimensions (W x H x D)

150 x 85 x 160mm


1.71 kg (3.77 lb)

Form Factor

ATX12V v2.53, EPS 2.92


10 Years

Power Specifications

Swipe to scroll horizontally
Max. PowerAmps202070.830.3
Total Max. Power (W)850

Cables & Connectors

Swipe to scroll horizontally
DescriptionCable CountConnector Count (Total)GaugeIn Cable Capacitors
ATX connector 20+4 pin (610mm)1116-20AWGYes
4+4 pin EPS12V (650mm)3318AWGYes
6+2 pin PCIe (600mm+150mm) 2416-18AWGYes
SATA (500mm+110mm+110mm+110mm)2818AWGNo
SATA (520mm+110mm+110mm)2618AWGNo
4-pin Molex (450mm+100mm+100mm+100mm)1418AWGNo
AC Power Cord (1400mm) - C13 coupler1118AWG-

The cables are long enough, and it is impressive to see three EPS and four PCIe available. There is no need for more PCIe, given that the majority of users have a single graphics card installed. The only letdown is the small distance between the peripheral connectors. 

Component Analysis

We strongly encourage you to have a look at our PSUs 101 article, which provides valuable information about PSUs and their operation, allowing you to better understand the components we're about to discuss.

Swipe to scroll horizontally
General Data-
Manufacturer (OEM)CWT
PCB TypeDouble Sided
Primary Side-
Transient Filter4x Y caps, 2x X caps, 2x CM chokes, 1x MOV
Inrush ProtectionNTC Thermistor SCK-037 (3 Ohm) & Relay
Bridge Rectifier(s) 2x GBU1506 (600V, 15A @ 100°C)
APFC MOSFETs 2x Vishay SiHF30N60E (650V, 18A @ 100°C, Rds(on): 0.125Ohm)
APFC Boost Diode 1x On Semiconductor FFSP0865A (650V, 8A @ 155°C)
Bulk Cap(s) 2x Nippon Chemi-Con (400V, 470uF each or 940uF combined, 2,000h @ 105°C, KMW)
Main Switchers 2x On Semiconductor FCPF190N60E (600V, 13.1A @ 100°C, Rds(on): 0.19Ohm)
APFC Controller Champion CM6500UNX & Champion CM03X
Resonant ControllerChampion CU6901VAC
Topology Primary side: APFC, Half-Bridge & LLC converter Secondary side: Synchronous Rectification & DC-DC converters
Secondary Side-
+12V MOSFETs6x On Semiconductor NTMFS5C430N (40V, 131A @ 100°C, Rds(on): 1.7mOhm)
5V & 3.3V

DC-DC Converters: 2x UBIQ QM3054M6 (30V, 61A @ 100°C, Rds(on): 4.8mOhm) & 2x UBIQ QN3107M6N (30V, 70A @ 100°C, Rds(on): 2.6mOhm) PWM Controllers: UPI Semi uP3861P

Filtering Capacitors

Electrolytic: 7x Nippon Chemi-Con (1-5,000h @ 105°C, KZE), 7x Nippon Chemi-Con (4-10,000h @ 105°C, KY), 1x Rubycon (4-10,000h @ @ 105°C, YXJ) Polymer: 37x FPCAP

Change Over Switch1x Sync Power SPN3006 MOSFET (30V, 57A @ 100°C, Rds(on): 5.5mOhm)
Supervisor ICWeltrend WT7502R (OVP, UVP, SCP, PG)
Fan ControllerMicrochip PIC16F1503
Fan ModelCorsair NR140ML (140mm, 12V, 0.27A, Magnetic Levitation Bearing Fan)
5VSB Circuit-
Rectifiers1x PS1045L SBR (45V, 10A) & IPS ISD04N65A (650V, 2.5A @ 100°C, Rds(on): 2.2 Ohm)
Standby PWM ControllerOn-Bright OB5282

Channel Well Technology (CWT) remains the OEM of the RMx line, and it did a great job under Corsair's strict supervision. The platform has some differences from the older one to provide increased efficiency at light loads and support for alternative sleep modes. The most important change is the new fan, with ML bearings. These fans do not come cheap, so it is a nice surprise that Corsair decided to use them in the new RMx line. 

The build quality is good overall. Corsair used Japanese capacitors on both primary and secondary sides, and known manufacturers provide the FETs. 

The transient/EMI filter has all necessary parts and it does a good job, in restricting EMI emissions. 

The two powerful bridge rectifiers are more than enough to handle the max power that this platform can deliver. 

The APFC converter uses two Vishay FETs and a single boost diode, by On Semiconductor. These are high-quality parts. 

The main switching FETs, provided by Infineon, are installed into a half-bridge topology. An LLC resonant converter is also used to boost efficiency. 

Six FETs regulate the 12V rail, and the minor rails are generated through a pair of DC-DC converters. 

The electrolytic caps are by Chemi-Con and Rubycon. Lots of polymer caps are also used, for ripple filtering. 

The 5VSB rail uses an SBR on its secondary side, so its efficiency will take a hit. 

Supervisor IC

(Image credit: Tom's Hardware)

The supervisor IC, a Weltrend WT7502R, is installed on the same board with the fan controller. 

Lots of polymer fans are installed on the face of the modular board, forming an addition ripple filtering layer. 

Soldering quality is good. 

The magnetic levitation fan is among the notable changes in the new RMx units. It isn't as quiet as the rifle bearing fan that the older RMx units use, but it is far more reliable, especially at high operating temperatures. 

MORE: Best Power Supplies

MORE: How We Test Power Supplies

MORE: All Power Supply Content

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.
  • Udyr
    What makes this unit better than the Toughpower GF1?
  • g-unit1111
    I have an RM750x and it is a really great PSU. You can't go wrong with this unit.
  • 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.
  • 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.
  • 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.
  • 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.