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Corsair RM750x (2021) Power Supply Review

The Corsair RM750x (2021) tops the performance charts.

Corsair RM750x (2021)
Editor's Choice
(Image: © Tom's Hardware)

Advanced Transient Response Tests

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

In the real world, power supplies are always working with loads that change. It's of immense importance, then, for the PSU to keep its rails within the ATX specification's defined ranges. The smaller the deviations, the more stable your PC will be with less stress applied to its components. 

We should note that the ATX spec requires capacitive loading during the transient rests, but in our methodology, we also choose to apply a worst case scenario with no additional capacitance on the rails. 

Advanced Transient Response at 20% – 20ms

VoltageBeforeAfterChangePass/Fail
12V12.037V11.814V1.85%Pass
5V5.041V4.974V1.33%Pass
3.3V3.293V3.200V2.82%Pass
5VSB5.027V4.971V1.11%Pass

Advanced Transient Response at 20% – 10ms

VoltageBeforeAfterChangePass/Fail
12V12.037V11.839V1.64%Pass
5V5.042V4.968V1.47%Pass
3.3V3.293V3.196V2.95%Pass
5VSB5.027V4.978V0.97%Pass

Advanced Transient Response at 20% – 1ms

VoltageBeforeAfterChangePass/Fail
12V12.037V11.848V1.57%Pass
5V5.041V4.954V1.73%Pass
3.3V3.293V3.197V2.92%Pass
5VSB5.027V4.954V1.45%Pass

Advanced Transient Response at 50% – 20ms

VoltageBeforeAfterChangePass/Fail
12V11.983V11.875V0.90%Pass
5V5.035V4.967V1.35%Pass
3.3V3.290V3.193V2.95%Pass
5VSB5.014V4.961V1.06%Pass

Advanced Transient Response at 50% – 10ms

VoltageBeforeAfterChangePass/Fail
12V11.984V11.882V0.85%Pass
5V5.035V4.963V1.43%Pass
3.3V3.290V3.190V3.04%Pass
5VSB5.014V4.957V1.14%Pass

Advanced Transient Response at 50% – 1ms

VoltageBeforeAfterChangePass/Fail
12V11.983V11.886V0.81%Pass
5V5.035V4.966V1.37%Pass
3.3V3.290V3.188V3.10%Pass
5VSB5.014V4.960V1.08%Pass

Voltage drops at 12V with transient loads are not so high, but the competition performs better here. The minor rails register better performance in these tests. 

Turn-On Transient Tests

In the next set of tests, we measure the PSU's response in simpler transient load scenarios—during its power-on phase. Ideally, we don't want to see any voltage overshoots or spikes since those put a lot of stress on the DC-DC converters of installed components.

There is only a tiny voltage overshoot at 5VSB, which is nothing to worry about. The 12V waveforms are (almost) perfect. 

Power Supply Timing Tests

There are several signals generated by the power supply, which need to be within specified, by the ATX spec, ranges. If they are not, there can be compatibility issues with other system parts, especially mainboards. From year 2020, the PSU's Power-on time (T1) has to be lower than 150ms and the PWR_OK delay (T3) from 100 to 150ms, to be compatible with the Alternative Sleep Mode.

PSU Timings Table
T1 (Power-on time) & T3 (PWR_OK delay)
LoadT1T3
20%51ms135ms
100%49ms137ms

The PWR_OK delay is within the 100-150ms region, so the PSU supports the alternative sleep mode recommended by the ATX spec.

Ripple Measurements

Ripple represents the AC fluctuations (periodic) and noise (random) found in the PSU's DC rails. This phenomenon significantly decreases the capacitors' lifespan because it causes them to run hotter. A 10-degree Celsius increase can cut into a cap's useful life by 50%. Ripple also plays an important role in overall system stability, especially when overclocking is involved.

The ripple limits, according to the ATX specification, are 120mV (+12V) and 50mV (5V, 3.3V, and 5VSB).

Test12V5V3.3V5VSBPass/Fail
10% Load4.5 mV3.3 mV3.3 mV4.9 mVPass
20% Load4.9 mV3.6 mV3.0 mV4.9 mVPass
30% Load8.1 mV3.5 mV3.3 mV5.2 mVPass
40% Load6.9 mV3.5 mV3.0 mV4.9 mVPass
50% Load6.4 mV3.8 mV3.1 mV5.0 mVPass
60% Load6.3 mV6.8 mV9.7 mV7.3 mVPass
70% Load6.1 mV4.0 mV3.5 mV5.4 mVPass
80% Load6.1 mV4.5 mV6.2 mV5.3 mVPass
90% Load5.9 mV4.3 mV7.6 mV5.3 mVPass
100% Load8.9 mV5.0 mV6.8 mV7.3 mVPass
110% Load9.0 mV5.1 mV9.8 mV6.4 mVPass
Crossload 15.3 mV4.6 mV7.9 mV6.1 mVPass
Crossload 29.3 mV4.5 mV3.7 mV5.8 mVPass

Ripple suppression is perfect! 

Ripple At Full Load

Ripple At 110% Load

Ripple At Cross-Load 1

Ripple At Cross-Load 2

EMC Pre-Compliance Testing – Average & Quasi-Peak EMI Detector Results

Electromagnetic Compatibility (EMC) is the ability of a device to operate properly in its environment without disrupting the proper operation of other nearby devices.

Electromagnetic Interference (EMI) stands for the electromagnetic energy a device emits, and it can cause problems in other nearby devices if too high. For example, it can be the cause of increased static noise in your headphones or/and speakers.

(Image credit: Tom's Hardware)

The conducted EMI emissions are within the specified limits. 

MORE: Best Power Supplies

MORE: How We Test Power Supplies

MORE: All Power Supply Content

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

  • RAZ0RLIGHT
    Is there any reason why the 2021 revisions fan curve is so much more aggressive?
    This would be the perfect Gold PSU if they would have implemented the same fan curve as the older 2018 revision.
    Reply
  • I
    RAZ0RLIGHT said:
    Is there any reason why the 2021 revisions fan curve is so much more aggressive?
    This would be the perfect Gold PSU if they would have implemented the same fan curve as the older 2018 revision.
    Disagree. It's still very quiet and I'd rather a tiny noise increase to reduce temps, increase lifespan.

    This is probably what Corsair determined as well through wear testing, decided that not only would that reduce their warranty fulfillment costs but also improve customer satisfaction by having a longer lasting product.

    If you don't care about the warranty, crack it open, put a few tens of ohms 2W resistor in series on the fan power lead, or just swap in a lower RPM fan, or mod the fan control circuit, or wear earplugs, or put the system under your desk, or get a cat plus 100 mice let loose all at once and you'll never even notice the very slight fan noise.

    Besides, it's all a bit silly. If your system is pulling that many amps it's going to need its own more audible fans running anyway. For good lifespan. An internal, reward-facing exhaust, oriented fan is the least audible way to pull or push air through a system.
    Reply
  • Russll
    Hello
    A few days ago I bought a Corsair RM750x (2021). Now the power supply consumes little (20-30%) because it works without a video card (AMD 5700G only).

    The Aida64 and OCCT show voltage on rail +12V - 11.884V, and on rail +3.3VCC - 3.248V, on rail +5V - 4.980V (computer idle, browser only).

    In the game, the voltage rises and shows on rail + 12V - 11.980V (maximum), and on rail + 3.3VCC - 3.264V (maximum), on rail + 5V - 5.020V.

    Is this normal at all.?
    There is no full 12V on rail + 12V, and no full 3.3V on rail + 3.3V..
    Maybe I should return the product to the store.?

    Reply
  • drivinfast247
    Russll said:
    Hello
    A few days ago I bought a Corsair RM750x (2021). Now the power supply consumes little (20-30%) because it works without a video card (AMD 5700G only).

    The Aida64 and OCCT show voltage on rail +12V - 11.884V, and on rail +3.3VCC - 3.248V, on rail +5V - 4.980V (computer idle, browser only).

    In the game, the voltage rises and shows on rail + 12V - 11.980V (maximum), and on rail + 3.3VCC - 3.264V (maximum), on rail + 5V - 5.020V.

    Is this normal at all.?
    There is no full 12V on rail + 12V, and no full 3.3V on rail + 3.3V..
    Maybe I should return the product to the store.?

    Perfectly normal operation.
    Reply
  • Russll
    drivinfast247 said:
    Perfectly normal operation.
    Thanks, I hope everything goes well.
    Reply