Corsair's line of RMx power supplies are renowned for their compact dimensions and quiet operation, but not their low prices. With an MSRP of $119.99 (£109.99), the new Corsair RM850 promises similar performance and acoustics to the more-expensive RM850x, but at a more affordable price point. However, to cut costs, Corsair has used lower-quality capacitors and a lesser cooling fan. These compromises result in a PSU that's not quite as quiet as its big brother, but could be a good choice if the street price is significantly lower.
Corsair's new RM (without the "x") line consists of three members with capacities ranging from 650W to 850W. All of them are more affordable versions of the corresponding RMx models, which we expect to be updated in the near future to be fully compatible with the latest ATX specification. The RM units mostly use Chinese Elite caps, which are of decent quality, instead of the superior Japanese Nichicon and Chemi Cons and employ Hong Hua rifle bearing fans instead of Corsair's more-powerful NR135L. These changes might not be welcome by PSU enthusiasts, but the fact is that they don't seem to affect the product's lifetime since Corsair provides exactly the same warranty period (ten-years), in both RM and RMx units.
Two new features of the RM units, which are not present in the RMx 2018 line, are the increased efficiency under very light loads (2% of the max-rated-output) and support for Windows 10’s new Modern Standby mode that enhances boot speed and connectivity for your PC. The S3 sleep state usually takes anywhere from 7-15 seconds to turn on depending on your PC's configuration, while the Modern Standby function promises to bring that to reliably under five seconds.
The RM850 is a fully modular power supply and contrary to the RM850x, it doesn't use in-cable caps which might offer better ripple suppression, but also make the cables bulky rendering the cable management process harder. The unit features semi-passive operation which, unfortunately, cannot be deactivated. This means that the power supply should not be used in chassis where the PSU compartment is sealed or with the fan grille facing downwards, because the hot air will be trapped at the PSU's internals causing high stress to its parts.
It might be an affordable version of the RMx line, but the RM850 has two EPS and six PCIe connectors so it will easily support a potent gaming system. Only the PCIe cables use thicker 16AWG gauges, up to the first connector, for lower voltage drops under high loads. There are no in-cable caps for better ripple suppression, while the distance between the peripheral connectors is too small at 100mm. Ideally, it should be 150mm.
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The manufacturer of the new RM units is the same with the RMx ones, Channel Well Technology or CWT in short. Compared to the more expensive RM850x, the RM850 has Elite bulk caps of lower overall capacity and we also notice a new resonant controller, the Champion CM6901V. The main difference with the popular CM6901TX is the kick mode, as Champion calls the burst mode, which allows the CM6901V to offer high efficiency under very light loads. With Intel preparing to push the efficiency notably higher under very light loads (60% or higher with 10W load for PSUs with 500W or less capacity and 2% of the max-rated-output for PSUs with higher than 500W capacity), Corsair had to make some changes in this platform to meet the upcoming requirements and the most important is the CM6901V resonant controller.
On the secondary side, we find several Elite electrolytic caps along with a pair of Suncon caps. There are some polymer caps as well, to help in ripple filtering. Finally, the next most important difference with the RM850x is the use of a different fan which is provided by Hong Hua. According to Corsair this fan also uses a rifle bearing, so most likely it won't have a problem in the long run, but still we prefer the NR135L fan that the RMx models use.
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