Introduction

We would like to thank Corsair for supplying the review sample.


After almost three years in production, Corsair decided to update its popular RMx line. There are again five members with capacities ranging from 550 W to 1000 W. All are fully modular, and the OEM is still Channel Well Technology. Listed below are the crucial changes over the RMx 2018 units with the RMx 2021 revision:

• Magnetic levitation fan for increased lifetime under high operating temperatures
• Modern standby compatibility for fast wake from sleep times
• High efficiency under very light and light loads
• Three EPS connectors with the 1000 W and 850 W units
• Cybenetics and 80 PLUS (in the reviewer's guide) certifications

This is the first time I see an ML fan in a power supply. This is excellent news because this bearing has the great endurance of double ball-bearings under high operating temperatures and the low noise output of a fluid dynamic bearing. The only downside is the higher cost. Another first for the new RMx is the number of EPS connectors. Who will ever need three of these connectors? This is too much power for nothing but the CPU socket area. Corsair must know something we aren't privy to. Utilizing three EPS connectors fully would need the CPU to draw 1 kW!

The Corsair RM850x is the second-strongest member of the line, suitable for strong gaming systems since it can support all high-end AMD and Intel CPUs along with such power-hungry cards as the RTX 3080, RTX 3090, RX 6800 XT, and RX 6900 XT. If you plan to overclock a system with similar specifications considerably, you are better off with the RM1000x.

Specifications

Photos

The box is relatively small, and at its face is a photo of the RMx 850 W PSU, with the 80 PLUS and warranty badges in the bottom-right corner.


Packing protection is adequate, and the bundle includes the necessary paperwork and mounting screws, along with several zip ties and modular cables.


The exterior design has changed, and both fan grille and front exhaust look better now because of triangular openings.


The power specifications label resides on the bottom.


The modular panel includes twelve sockets.


Some more photos of the power supply.

Cables and Connectors

Three EPS connectors and four PCIe are all available at the same time! A large number of peripheral connectors are present as well. Finally, in-cable capacitors have been put on the main ATX, EPS, and PCIe cables.


All cables are black, and the ATX, EPS, and PCIe cables are fully sleeved.


All peripheral cables are flat (ribbon style).

Component Analysis

Before reading this page, we strongly suggest a look at this article, which will help you understand the insides of a PSU better.



The platform is by CWT, and after a quick first glance, it looks the same as the older RM850x platform, but there are several differences. The components CWT used are of high quality, and the same goes for the magnetic levitation bearing fan. Japanese manufacturers provide all the caps, and a great number of polymer caps are used as well. Lastly, since PCB dimensions are regular, there is plenty of space between components, so airflow is unobstructed.


The transient filter has all the necessary components to deal with voltage surges, and suppresses incoming and outgoing EMI emissions.


Large inrush currents are suppressed by an NTC thermistor and bypass relay combination, which does a fine job.


The two bridge rectifiers can handle up to 30 A of current.


The APFC converter's FETs are provided by Vishay, so they are of top quality. The same goes for the boost diode, which is strong enough for the job. Finally, the bulk caps are provided by Chemi-Con and have enough capacity to provide a hold-up time of over 17 ms.


Two On Semiconductor FETs installed in a half-bridge topology are the main FETs.


The APFC controller is the Champion CM6500UNX, and a CM03X IC supports it.


The LLC resonant controller is a Champion CU6901VAC.


The FETs that regulate the +12 V rail are six On Semiconductor NTMFS5C430Ns. They are installed on a vertical board close to the main transformer.


Two DC-DC converters generate the minor rails. They use four UBIQ FETs, and the common PWM controller is a UPI Semi uP3861P.


The electrolytic caps are provided by Chemi-Con and Rubycon, and there are loads of polymer caps by FPCAP, which are much more tolerant to high operating temperatures.


The 5VSB circuit uses a PS1045L SBR on its secondary side, and the standby PWM controller is an On-Bright OB5282 IC. Once the PSU starts, the 5VSB rail takes power from the 5 V rail. This is done through a change-over switch, a Sync Power SPN3006 FET.


There are lots of polymer caps on the modular board's face.


Soldering quality is good, but the PCB's finish could be better.


Two closeups of the PCB's solder side.


This board hosts the supervisor IC and fan controller, a Microchip PIC16F1503 IC, which allows for precise speed control.


The cooling fan is a Corsair NR140ML. It has a diameter of 140 mm and uses a magnetic bearing.