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Corsair RM850 Power Supply Review: A Solid Value

Transient Response Tests, Ripple Measurements and EMC Pre-Compliance Testing

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 extra capacitance on the rails. 

Advanced Transient Response at 20% – 200ms


Advanced Transient Response at 20% – 20ms


Advanced Transient Response at 20% – 1ms


Advanced Transient Response at 50% – 200ms


Advanced Transient Response at 50% – 20ms


Advanced Transient Response at 50% – 1ms

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The transient response of the +12V rail is satisfactory and the same applies to the 5V and 5VSB rails. On the contrary, there is (a lot of) room for improvement on the 3.3V rail, which failed in most 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.

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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).

10% Load4.9 mV6.4 mV9.1 mV7.2 mVPass
20% Load10.6 mV7.2 mV11.2 mV8.2 mVPass
30% Load7.6 mV8.1 mV11.3 mV8.3 mVPass
40% Load9.3 mV9.4 mV11.6 mV8.4 mVPass
50% Load9.1 mV9.3 mV11.6 mV8.0 mVPass
60% Load9.6 mV10.4 mV13.2 mV8.4 mVPass
70% Load10.6 mV11.2 mV13.9 mV8.5 mVPass
80% Load11.7 mV11.6 mV15.1 mV9.3 mVPass
90% Load12.5 mV12.5 mV16.6 mV8.7 mVPass
100% Load16.8 mV14.8 mV16.6 mV11.0 mVPass
110% Load17.8 mV14.5 mV18.6 mV11.0 mVPass
Crossload 118.8 mV10.7 mV16.6 mV8.9 mVPass
Crossload 217.8 mV11.4 mV15.5 mV10.2 mVPass
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The ripple suppression might not be at the perfect levels that the RM850x achieves, because the RM850's modular cables don't use any in-cable caps, but still is very good

Ripple At Full Load

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Ripple At 110% Load

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Ripple At Cross-Load 1

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Ripple At Cross-Load 2

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EMC Pre-Compliance Testing – Average & 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 close-by devices.

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

The conducted EMI emissions are low, throughout the entire frequency range that we measured (150KHz - 30MHz).

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