Corsair CS850M 850W Power Supply Review

Early Verdict

With the current price tag, Corsair's CS850M faces tough competition. The PSU offers decent performance and high efficiency, however a small price drop would make it a much better buy.


  • +

    • Full power at 48 °C • Performance • Silent operation • Efficiency • Dimensions


  • -

    • Price • Polymer cap quality • No MOV in EMI filter • Hold-up time • Advanced Transient Response • Single EPS connector • Warranty

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Corsair CS850M Power Supply Review

Many enthusiasts don't have the budget for a flagship power supply, but still crave high efficiency to save money on electricity. They want enough capacity for a couple of powerful graphics cards, plus modular cables for trouble-free installation. Corsair's CS850M seems to fit this description. On top of that, it offers decent performance.

Corsair has a lot of power supplies in its portfolio, covering almost every conceivable market segment. Its CS family sits between the CX(M) and RM series. According to the company, it's above the mainstream line-up, addressing power users who want something better than a 80 PLUS Bronze-rated unit.

There are five CS models with capacities ranging from 450 to 850W. All of them sport 80 PLUS Gold efficiency, feature semi-modular cabling with low-profile and black modular cables and utilize Japanese primary capacitors. Those primary caps help ensure high reliability, though the secondary side's caps are critical as well (we'll discuss them all in more detail). The CS models are covered by three-year warranties since they occupy a lower tier of Corsair's power supply hierarchy. The higher-end models include five- to seven-year coverage. With this PSU, you get what you pay for. If warranty coverage is a big priority for you, consider buying a beefier unit.

In this review, we're looking at the CS line's highest-output implementation. According to Corsair, the CS850M is ideal for moderate gaming, though we know it'll drive a machine with two powerful graphics cards installed. Clearly, the folks at Corsair believe that anyone interested in a CS model will want it for lower power consumption and a more conservative price tag. The reality is that if you leave your PC on all day, even at low loads, an 80 PLUS Gold-rated PSU could save you enough money over time to justify its purchase.

You probably won't see a noticeable difference switching from an 80 PLUS Gold PSU to a Platinum one, but the difference between an 80 PLUS Bronze and Gold-rated unit is significant. In addition, PSUs age. After years of continuous use, their performance degrades. If they employ high-quality capacitors, this process is slow. But if they use cheaper Chinese caps, the loss of performance is more severe as time passes. And once an old PSU stops working, it can take out other components in your system. So pay attention to sudden restarts and stability problems as your PSU gets older.


The CS850M's efficiency is enough to meet the 80 PLUS Gold requirements, and it utilizes a semi-modular design with only two fixed cables. Like most PSUs in this price range, the CS850M is Haswell-ready, meaning that it can deliver full load on the minor rails with minimum load at +12V, with all of its rails within the ATX specification's ranges.

Corsair specs a maximum operating temperature of 40 degrees C. You won't be able to abuse this PSU because it doesn’t use high-quality capacitors like the company's higher-end models. All of the protections we look for are enabled except for over-current protection (which simply isn't needed in a high-capacity single-rail power supply). A sleeve bearing fan is tapped for cooling, since ball-bearing fans are more expensive and Corsair wants to keep the price of this unit as low as possible. Finally, the dimensions of the PSU are compact and the provided warranty of three years is satisfactory for a mid-category PSU, although a longer warranty would have been nice.

Power Specifications

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Max. PowerAmps252570.830.8
Total Max. Power (W)850

There is only one +12V rail, which can deliver almost 71A. Again, it should drive a fairly high-end PC with a couple of potent graphics cards installed. The minor rails offer up to 130W combined power, which is ample for any modern PC. The 5VSB rail is powerful enough for the needs of an average user.

Cables And Connectors

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Native Cables
ATX connector (620mm)20+4 pin
4+4 pin EPS12V (670mm)1
Modular Cables
6+2 pin PCIe (600mm+150mm)4
SATA (500mm+95mm+95mm+95mm)8
4 pin Molex (450mm+100mm+100mm)6

Only two cables are fixed, which is fine since they're essential for every new PC build anyway. Cable length is adequate overall, though the distance between the four-pin Molex connectors could be problematic. Typically, the components powered by these connectors are far from each other (think case fans). But Corsair puts them fairly close together. On the plus side, short runs between the SATA connectors are ideal since hard drives and SSDs are typically right next to each other. Finally, all connectors use 18AWG wires, which are recommended by the ATX spec.

The number of PCIe, SATA and four-pin Molex connectors is good, given this unit's capacity. However, Corsair equips the CS850M with just one EPS connector. Normally, an 850W PSU should have two of them. In addition to server-oriented mainboards, some X99 platforms also require two EPS connectors (or one EPS and one ATX12V). If you plan to use this PSU with one of those motherboards, you'll need to use adapters, and we try to avoid those. Lots of current can pass through EPS and PCIe cables, and the use of adapters can lead to problems. Four-pin Molex connectors are used to attach adapters, and they were designed for such high amperage. On top of that, using adapters leads to increased wire resistance. In short, if your machine needs two EPS connectors or more PCIe connectivity, buy a PSU that covers those requirements. 

Power Distribution

Since this PSU features a single +12V rail, there isn’t much to say about its power distribution.

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Contributing Editor

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.

  • codygriffy
    Looks very nice!
  • Shneiky
    Another CS PSU with bad caps and short life. And at 120 USD or more than 120 EUR as it appears in my district, this PSU does not stand a chance against the competition. Still a lot of people will buy it just because it has a Corsair name on it. I feel kinda bad that Corsair ruins their legacy of quality with products like CS and VS.
  • giantbucket
    15746324 said:
    Another CS PSU with bad caps and short life. And at 120 USD or more than 120 EUR as it appears in my district, this PSU does not stand a chance against the competition. Still a lot of people will buy it just because it has a Corsair name on it. I feel kinda bad that Corsair ruins their legacy of quality with products like CS and VS.

    and then there are people who are going to hate on it just because it has a Corsair name on it...
  • ykki
    Nice review! Can Tom's start a psu rating system (on a scale of 1 to 10)?
  • Amdlova
    this perform really bad
  • endeavour37a
    ykki, here is a tier list of PSUs, perhaps this is what your talking about.......
  • Sakkura
    Breaks ATX spec, high-ish 12V ripple, bad capacitors... No thanks.
  • Shneiky

    I do not hate Corsair products because they are Corsair. I have a Corsair K70 and I love it. What I hate is cheaply made equipment that wants a price premium because it is X brand.
  • Aris_Mp
    @ykki The relative performance graph can play this role and with much more accuracy. However it measures pure performance and doesn't take into account other factors as output noise, warranty period etc. For these factors a final rating is needed, indeed.
  • damric
    Good review, Aris.

    I see no reason to buy this PSU when there are other good units with lower price built with better components. Example: Many XFX (Seasonic) and Golden Green (Capstone/B2) cost less but are more reliable with all good caps. Unfortunately, most consumers will be suckered in by the Corsair sticker.

    On the bright side, these Great Wall units have far less problems than the CX series. Probably even more reliable than the RM.