Cold Test Results (Room Temperature)

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M 40 MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs - 2014 Pipeline post.

The new Corsair HX850 falls a little short regarding its 80Plus Platinum certification, failing to achieve >94% efficiency at 50% load with an input voltage of 230 VAC. This result however does not mean that the unit’s certifications are false, just that it received its efficiency rating with an input voltage of 110 VAC, under which the 80Plus directive is slightly more lenient. Also note that our ambient temperature is a little higher than the 25 °C recommended by the directive. Despite that, the HX850 has a very high average efficiency of 92.7% within its nominal load range (20% to 100% of the unit's capacity) and gave us fairly good efficiency readings under low loads.

The high efficiency of the Corsair HX850 allows the thermally controlled fan to stay inactive for a very large portion of the load range when the unit is operating in room temperature. Our test sample reached an output of nearly 400 Watts before the fan started to spin. The fan was relatively quiet thorough the entirety of our room temperature testing, reaching high noise figures only when very heavily loaded.

External Inspection, Package and Contents Hot Box Test Results


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  • BurntMyBacon - Wednesday, October 25, 2017 - link

    I should probably mention that there are a few different versions of prime supply differentiated by efficiency:



  • evilspoons - Tuesday, October 24, 2017 - link

    As a Canadian who has to translate from USD to CAD all the time mentally, I'm always surprised when I find out you review your power supplies at 230V/50Hz (i.e. not in North America). I guess you get to do that bit of mental translation too.

    Good to know the Corsair supplies are still solid. I've had an HX750 since I bought my i7-2600k and it ran SLI 680s and an overclocked CPU since whenever that was. The 680s have since been replaced with a 1080 but if I ever need a PSU, shouldn't be too hard to choose...
  • Morawka - Tuesday, October 24, 2017 - link

    It's funny how we've come full circle with power supplies. At first a Single 12V rail was desirable but nowadays, a Multiple rail system is preferred with the advent of virtual rails. I have a question. I have a RMI 1000x PSU from Corsair which also has Single and Multi-rail options. So is it generally preferred to keep it operating in multi-rail mode? Could a single 1080Ti or a 7900X CPU OC'd for example -- go over the 40A rating. (I think the RMi1000 has the same multi-rail setup as this one, albiet more rails.) Reply
  • TheWereCat - Tuesday, October 24, 2017 - link

    1080ti can go easily to 40A when you unlock the power and voltage limit. Not by default as most if not all cards have power limit at around 355W.
    I flashed my FTW3 with XOC BIOS and I am easily hitting 400W (I am using the FTW3 air cooler) so I don't dare to push the card more even if I could but then the very high temps would lower my clocks significantly so it would be pointless.
  • DanNeely - Tuesday, October 24, 2017 - link

    Yup. We started with multiple rails due to a max current safety requirement. Then PSU makers started ignoring that limit and making single giant rails. The standard was updated to allow this. (Were any compensatory safety requirements added?) The safety benefits from smaller overcurrent limits never went away though, so now we're seeing them added back to individual outputs.

    It'll be interesting to see if the PSUs that have an internal USB2 header cable and a control app let you customize the max for each output port separately instead of being a single all or nothing option.
  • Morawka - Tuesday, October 24, 2017 - link

    I'll let you known if that's possible here in a couple of days as i'm building a 7900x with a RM1000i Power supply w/ Corsair Link. Being able to set the max amperage per 12v rail would be ideal for enthusiast. Reply
  • jonnyGURU - Monday, October 30, 2017 - link

    To clarify.. we started with multiple +12V rails until PC Power & Cooling, at the time one of the largest PSU vendors, screwed up and didn't split rails up accordingly for their Turbo-Cool line. Instead of correcting the issue, they went rogue and said "screw this rail B.S.! Make everything single +12V rail!!!" Because their marketing was so strong, they brainwashed everyone into believing that the mistake wasn't on their end and so all the other vendors had to switch to single +12V rail as well to maintain their market share. Reply
  • FaaR - Wednesday, November 1, 2017 - link

    I think you'd have to work hard to make a single GPU pull over 480W of power (;P), but if this worries you, just attach two power cables from different (virtual) rails for a total of 80 amps DC to your GPU.

    Of course, an 850W PSU isn't going to be able to supply that much juice just to your GPU, but you knew that already of course. :)
  • gammaray - Tuesday, October 24, 2017 - link

    so if the HX serie is for "overclockers and advanced enthusiasts" what is the AX and RM series for? Reply
  • Morawka - Tuesday, October 24, 2017 - link

    Corsair Link seems to be the separating feature. Well that and type 4 PSU cables that reduce voltage droop by implementing capacitors along each 12v wire. The RM series are mostly Gold certified whereas the AX series utilizes platinum efficiency with a Digital switching controller (also missing from the TX line) Reply

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