Corsair RM850x (2024)

The Corsair RM850x (2024) is an 850-watt, fully modular ATX power supply from Corsair's RMx Series, which the company describes as its best-selling PSU, updated. The current generation is certified for ATX 3.1, includes a native 12V-2x6 graphics cable, and is rated Gold for efficiency and A for noise by the testing lab Cybenetics. It is a conventional-layout unit, with the cable sockets on the rear face, and it is the natural counterpart to Corsair's side-connector RM850x SHIFT. This page goes through the published specification, explains what each item means in a build and describes who the unit suits.

Power and rails

Corsair specifies 850 W of continuous power. The rail table lists +3.3 V at 20 A and +5 V at 20 A with a combined limit of 150 W, a single +12 V rail at 70.8 A, which is 849.6 W, and +5 V standby at 3 A for 15 W. The +12 V rail therefore carries essentially the whole rated output, as in most modern power supplies, because processors and graphics cards draw almost entirely from 12 V. The AC input range is 100 to 240 V at 10 A to 5 A and 47 to 63 Hz, so the unit works on either 115 V or 230 V mains. Corsair also rates the unit for 50 degrees Celsius continuous operating temperature, which it describes as ensuring reliable power even under high stress. The mean time between failures is 100,000 hours. Our guide to how much PSU wattage you need explains how to choose between 750 W, 850 W and 1000 W.

Efficiency and noise ratings

The unit carries Cybenetics ratings of Gold for efficiency and A for noise. Cybenetics is an independent testing organisation whose ETA grades rate efficiency and whose LAMBDA grades rate noise; a Gold efficiency grade and an A noise grade are Corsair's stated result for this model. The rating tells you about the behaviour of the unit across its load range and how much noise it makes under test conditions, both of which matter in a quiet build. The efficiency rating also determines how much heat the unit generates for a given load. Corsair does not list an 80 PLUS tier for this unit in the specification we reviewed, so we do not quote one.

ATX 3.1 and the native 12V-2x6 cable

The power supply is certified for ATX 3.1, and Corsair says this ensures compatibility with the latest sleep and hibernate modes and modern CPU and GPU requirements. The unit lists ATX12V version 3.1 and supports Modern Standby. A native 12V-2x6 cable, 650 mm long, is included for modern graphics cards, so no adapter is needed. Because this connector carries high current through a compact plug, seat it fully, avoid sharp bends near the connector and use the supplied cable. Our explainer on the 12VHPWR and 12V-2x6 connector describes the reasons. The graphics cable is supplemented by three individual PCIe 8-pin (6+2) cables of 650 mm each, so you can also power a graphics card that uses conventional 8-pin connectors.

Cables

The cables are Corsair Type 4 with an embossed finish and low-profile combs that keep the cables neat. The bundle contains one 24-pin ATX cable of 610 mm, two 8-pin EPS/ATX12V CPU cables (4+4) of 750 mm each, one 12V-2x6 cable of 650 mm, three PCIe 8-pin (6+2) cables of 650 mm, two SATA cables with four connectors each giving eight in total, and one PATA cable with three connectors. The 750 mm CPU cables are longer than those supplied with many power supplies, which helps in larger cases where the processor socket is far from the PSU shroud. With eight SATA connectors and one PATA cable, the unit covers most drive setups. If you need more, Corsair sells individually sleeved cable kits for Type 4 units.

Cooling and noise control

The fan is 140 mm with a fluid dynamic bearing and a magnetic dome structure, which Corsair says keeps noise to a minimum. A Zero RPM mode stops the fan completely at low to medium loads. A feature that distinguishes this unit is the manual fan override knob: it lets you override the Zero RPM mode and low-noise profile and increase fan speed and airflow if you want to pull more air through the power supply or exhaust more heat from the case. The unit uses 100 percent industrial-grade Japanese electrolytic capacitors rated for 105 degrees Celsius. For advice on building a system that stays quiet under load, see our silent PC build guide.

Dimensions and installation

The unit measures 160 mm by 150 mm by 86 mm and weighs about 3 kg. Those are standard ATX power supply dimensions, with a moderate depth that fits most current cases. Because the sockets are on the rear face, cable installation follows the conventional route through the back of the case, and the unit works in cases of the usual design without special access needs. The main compatibility question is simply whether your case takes an ATX supply and whether its cable-management space can hold the flat cables comfortably.

Choosing 850 W

The RMx range is offered at 750 W, 850 W and 1000 W. To give a published reference point for sizing, NVIDIA lists 650 W as the required system power for the GeForce RTX 5070 and 750 W for the GeForce RTX 5070 Ti, in both cases for a PC with a Ryzen 9 9950X processor. An 850 W supply leaves room above those figures for a high-end processor, several drives and a case full of fans, and it gives headroom if you later change to a more demanding graphics card. As with any supply, running well below the maximum rating usually means lower fan speed and less noise, and combined with the Zero RPM mode it is often what keeps a system silent at idle.

Warranty and price

Corsair backs the RM850x with a ten-year warranty. Prices change with promotions and by region, so we do not quote one. Compared with the older budget Corsair CX600M, the RM850x offers higher capacity, full modularity, higher efficiency and ATX 3.1, at a correspondingly higher price. To see how it differs from the side-connector version, use the RM850x SHIFT versus RM850x comparison, and to look at other units, browse power supplies.

Who should consider it

The RM850x (2024) suits a mainstream or high-end gaming or workstation build that needs a quiet, dependable 850 W supply with a native 12V-2x6 cable and does not require the SHIFT side-connector layout. It is a sensible default for builders who want a widely supported, conventional unit with a long warranty. All specifications come from Corsair's product page; availability and prices vary by region.

Product image: CORSAIR product image.