Corsair RM750x PSU Review

Transient Response Tests And Ripple Measurements

Advanced Transient Response Tests

For details on our transient response testing, please click here.

In these tests, we monitored the response of the PSU in two different scenarios. First, a transient load (10A at +12V, 5A at 5V, 5A at 3.3V and 0.5A at 5VSB) was applied to the PSU for 200 milliseconds while the PSU was working at 20-percent load. In the second scenario, the PSU was hit by the same transient load while operating at 50-percent load. In both tests, we used our oscilloscope to measure the voltage drops caused by the transient load. The voltages should have remained within the ATX specification's regulation limits.

These tests are crucial because they simulate the transient loads a PSU is likely to handle (such as booting a RAID array, an instant 100-percent load of CPU/GPUs, etc.). We call these tests Advanced Transient Response Tests, and they are designed to be very tough to master, especially for a PSU with a capacity of less than 500W.   

Advanced Transient Response at 20 Percent

VoltageBeforeAfterChangePass/Fail
12V12.048V11.971V0.64%Pass
5V5.042V4.976V1.31%Pass
3.3V3.317V3.213V3.14%Pass
5VSB5.016V4.967V0.98%Pass

Advanced Transient Response at 50 Percent

VoltageBeforeAfterChangePass/Fail
12V11.984V11.910V0.62%Pass
5V5.037V4.968V1.37%Pass
3.3V3.309V3.199V3.32%Pass
5VSB5.000V4.946V1.08%Pass

The +12V rail behaved very well during these tests, and the 5V and 5VSB rails kept their voltage drops at low levels. On the other hand, the 3.3V rail didn't manage to keep its voltage above 3.2V during the second test, although its deviation was at normal levels (for this rail).

Here are the oscilloscope screenshots we took during the Advanced Transient Response Tests:

Transient Response At 20 Percent Load

Transient Response At 50 Percent Load

Turn-On Transient Tests

In the next set of tests, we measured the response of the PSU in simpler transient load scenarios — during the PSU's power-on phase.

For the first measurement, we turned off the PSU, dialed in the maximum current the 5VSB could output and switched on the PSU. In the second test, we dialed the maximum load the +12V could handle and started the PSU while it was in standby mode. In the last test, while the PSU was completely switched off (we cut off the power or switched off the PSU by flipping its on/off switch), we dialed the maximum load the +12V rail could handle before switching on the PSU from the loader and restoring the power. The ATX specification states that recorded spikes on all rails should not exceed 10 percent of their nominal values (+10 percent for 12V is 13.2V, and 5.5V for 5V).    

A tiny voltage overshoot at the 5VSB rail and two small waves on the waveform before the +12V rails settle down during the last test are nothing to worry about. Overall, the PSU showed good performance here.

Ripple Measurements

To learn how we measure ripple, please click here.

The following table includes the ripple levels we measured on the rails of the RM750x unit. The limits, according to the ATX specification, are 120mV (+12V) and 50mV (5V, 3.3V and 5VSB).

Test12V5V3.3V5VSBPass/Fail
105.3 mV6.1 mV7.3 mV20.7 mVPass
205.7 mV6.0 mV7.5 mV4.0 mVPass
306.8 mV5.6 mV7.8 mV4.3 mVPass
407.0 mV5.7 mV9.8 mV5.2 mVPass
507.6 mV6.1 mV9.6 mV6.1 mVPass
608.5 mV6.6 mV11.2 mV6.9 mVPass
709.3 mV7.6 mV11.9 mV8.2 mVPass
8010.5 mV8.4 mV12.8 mV10.4 mVPass
9011.3 mV9.0 mV13.6 mV10.6 mVPass
1013.3 mV10.7 mV16.9 mV11.9 mVPass
1114.1 mV11.0 mV18.3 mV12.7 mVPass
CL18.0 mV9.6 mV10.8 mV6.9 mVPass
CL212.7 mV10.7 mV16.7 mV11.3 mVPass

We saw excellent ripple suppression on all rails. This platform is a great performer, thanks to Corsair's interventions. Besides the high-quality capacitors on the main PCB, the extra capacitors on the ATX, EPS and PCIe cables likely did their part as well.

Ripple Oscilloscope Screenshots

The following oscilloscope screenshots illustrate the AC ripple and noise registered on the main rails (+12V, 5V, 3.3V and 5VSB). The bigger the fluctuations on the screen, the bigger the ripple/noise. We set 0.01V/Div (each vertical division/box equals 0.01V) as the standard for all measurements.

Ripple At Full Load

Ripple At 110-Percent Load

Ripple At Cross-Load 1

Ripple At Cross-Load 2

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19 comments
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  • Blueberries
    I've been promoting these for a while, it's nice to see Tom's do an article on them. The only reason these are Gold rated is because they just miss the Platinum rating at 20%.

    They have a 650x as well that's a little cheaper.
  • Amdlova
    High Rate Faliure can be the the name of this series of corsair. for Now EVGA or SEASONIC power supplies. don't spend a penny on corsair products...
  • Aris_Mp
    Please keep in mind that some Corsair PSUs are also made by Seasonic. Also this series is very new to have a high rate of failures. Unless you have some solid facts to share on the older RM line which is out for quite some time now.
  • jonnyguru
    1335368 said:
    High Rate Faliure can be the the name of this series of corsair. for Now EVGA or SEASONIC power supplies. don't spend a penny on corsair products...


    Wrong on so many levels.

    YOU do not have the failure rate for this or any other Corsair PSU.

    This PSU is the RMx, not the RM, so even if you did have a failure rate, it would only be about two weeks of data.

    If you were talking about the RM and not the RMx, and you actually had failure rate data, you would see that the failure rate on the RM wasn't really high at all.
  • PureBlackFire
    Quote:
    High Rate Faliure can be the the name of this series of corsair. for Now EVGA or SEASONIC power supplies. don't spend a penny on corsair products...


    *sigh* nonsense comment of the day.
  • chalabam
    Tomshardware:

    I don't know if this is a problem of your site, or my PC/IP, but frequently the charts do not load, even when the page "ends" loading.



    Sometimes, if I "reload", then the charts also load.

    I open all the article pages simultaneously, on different tabs, so I don't need to wait for each one to load.
  • Rookie_MIB
    The older RM units weren't 'bad' really, they were ok, but Corsair has been stepping up its game with quality parts and build on some of these newer units which is nice to see. You can never have too many solidly designed units to choose from - competition toughens the breed.
  • Blueberries
    Quote:
    High Rate Faliure can be the the name of this series of corsair. for Now EVGA or SEASONIC power supplies. don't spend a penny on corsair products...


    Did you even LOOK at the article? The only problem with these are the Sinopowers on the secondary side, and that's not even a "bad" thing. Oh and btw, some of the best power supplies in the world are Superflower OEMs produced by Corsair.
  • mavikt
    With these in depth coverage of PSU's I propose introducing a tier'ing table thing at the and of each review (or perhaps a best buy PSU of the month) equivalent to what's done for CPU's and GPU's, ranking PSU models (perhaps too the makers). I saw a comment here on toms on another PSU news flash in the comment section referring to such thing in the forum but now I can't find it.
    Permanent'ing such thing from the editorial side would be great!
  • anort3
    Quote:
    Quote:
    High Rate Faliure can be the the name of this series of corsair. for Now EVGA or SEASONIC power supplies. don't spend a penny on corsair products...
    Did you even LOOK at the article? The only problem with these are the Sinopowers on the secondary side, and that's not even a "bad" thing. Oh and btw, some of the best power supplies in the world are Superflower OEMs produced by Corsair.


    Corsair doesn't use SuperFlower anywhere in its lineup. CWT, Great Wall, Flextronics, Seasonic and Chicony which has since been dropped are all the OEMs Corsair uses or has used.
  • JackNaylorPE
    Tier lists and OEM brand are by no means an indicator of quality. Just because a certain OEM is used is no guarantee of quality. Just like Corsair sells Great, Good, moderate and crappy PSU's, most OEMs also produce a wide range of quality.

    Tier lists will include an entire product line in a category based upon a single model review. The Corsair HX 750/850 were great, the 1000 / 1050 were dogs but all were placed in the same tier. Below we see that CWT made their lowest tier as well as some of the best products Corsair ever sold.

    CS was made by Great Wall
    CX and GS by CWT
    VS by CWT
    RM 450-650 were made by CWT,
    RM 750 and 850 by Chcony
    RM 750v2 -850v2 and 1000 were made by CWT
    RMi / RMx series are made by CWT
    HX 650 was made by Seasonic
    HX 750, 850 and 1050 were made by CWT (2/3 were excellent)
    HXi series was made by CWT
    AX series was made by Seasonic
    AXi was made by Flextronics
  • Blueberries
    218893 said:
    Quote:
    Quote:
    High Rate Faliure can be the the name of this series of corsair. for Now EVGA or SEASONIC power supplies. don't spend a penny on corsair products...
    Did you even LOOK at the article? The only problem with these are the Sinopowers on the secondary side, and that's not even a "bad" thing. Oh and btw, some of the best power supplies in the world are Superflower OEMs produced by Corsair.
    Corsair doesn't use SuperFlower anywhere in its lineup. CWT, Great Wall, Flextronics, Seasonic and Chicony which has since been dropped are all the OEMs Corsair uses or has used.


    Wrong. The AXi is a SuperFlower Leadex OEM. Which is sometimes produced by Corsair, Seasonic, and EVGA.
  • anort3
    The AXi OEM is Flextronics..... Unless you know something all the review sites don't?

    http://www.realhardtechx.com/index_archivos/Page447.htm

    http://www.orionpsudb.com/corsair

    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=317

    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=378


    And why would Seasonic make a SuperFlower platform? They don't. The 2 companies are direct competitors. You are correct about EVGA using SuperFlower though.
  • Blueberries
    I'll shut up now. I thought the AXi was SuperFlower which is the stem of my confusion
  • jonnyguru
    35894 said:
    The Corsair HX 750/850 were great, the 1000 / 1050 were dogs...


    They were?!?!?! Says who???
  • JackNaylorPE
    Quote:
    They were?!?!?! Says who???


    The guy who gave it a 8.5 performance * and 7.0 Build Quality rating :)
    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=245

    The 850 got a 10 in performance but back then no BQ ratings
    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=153

    * 1000 wasn't that bad with a 9.0 performance rating. I used it 3 times as I recall, had problems with 2..... one would hiccup under SLI loads, a user build had fan noise issues.
  • jonnyguru
    35894 said:
    Quote:
    They were?!?!?! Says who???
    The guy who gave it a 8.5 performance * and 7.0 Build Quality rating :) http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=245


    Right. And if you read the fine print:

    "More loose heatsink screws to deal with. But at least there were only two of them in there this time that could be considered a potential problem. Two points off for that. It'll probably never be a problem for 99% of these sold, but I'm an electronics tech. I get to be picky with stuff like that."

    This doesn't make a product "a dog".

    AFAIK, it really wasn't a problem for 99% of the folks out there and since it was pointed out in the reviews, CWT started using nylon washers or thread lock on all screws.
  • tacgnol06
    RM750i is currently slightly cheaper than this model on Newegg, which leads me to wonder why they'd release this version to begin with, unless they're phasing it out to replace it with something cheaper to make for around the same retail price... oh.
  • JackNaylorPE
    112719 said:
    Right. And if you read the fine print: "More loose heatsink screws to deal with. But at least there were only two of them in there this time that could be considered a potential problem. Two points off for that. It'll probably never be a problem for 99% of these sold, but I'm an electronics tech. I get to be picky with stuff like that." This doesn't make a product "a dog".


    I did read the fine print, but I am speaking "in context" ... As you said ... 2 points off... that only brings it to a 9. In the general context of things, I normally would call a 9.0 build quality rating a dog.... perfectly acceptable, perfectly suitable for an office or budget restricted gaming box.

    But when one is looking at, and prepared to pay for what the HX series bought to the table for a presumed moderate to higher end build for overclocking or gaming, the mindset is "top end".

    I expect a 10.0 here. When you are paying 10.0 quality a prices, a 9.0 BQ / Perf. rating is gonna get a "dog" label, at least in my eyes. If I wanted 9.0's, I'd look at cheaper model lines. As a TX, and without the careless assembly, the moniker would not have been used.