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Asus ROG Thor 1200W PSU Review: Asus Brings a Screen to the PSU Party

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

Advanced Transient Response Tests

For details on 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. 

Advanced Transient Response at 20 Percent – 200ms


Advanced Transient Response at 20 Percent – 20ms


Advanced Transient Response at 20 Percent – 1ms


Advanced Transient Response at 50 Percent – 200ms


Advanced Transient Response at 50 Percent – 20ms


Advanced Transient Response at 50 Percent – 1ms

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During the 20 percent load test, the PSU operates in PWM mode. Hence the voltage drops once we apply the transient load are increased. This is not the case with 50 percent load where the unit operates in FM mode. The overall performance is decent, though definitely not the best. With the added caps that the ATX spec requires, the transient response is vastly improved, especially on the minor rails.

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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We notice some tiny spikes here, but they're nothing to worry about.

Ripple Measurements

Ripple represents the AC fluctuations (periodic) and noise (random) found in the PSU's DC rails. This phenomenon significantly decreases the capacitors' life span because it causes them to run hotter. A 10 degree C increase can cut into a cap's useful life by 50 percent. 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% Load13.8 mV6.5 mV14.2 mV10.6 mVPass
20% Load13.6 mV7.0 mV14.7 mV10.7 mVPass
30% Load7.5 mV6.6 mV14.6 mV10.8 mVPass
40% Load7.7 mV7.3 mV15.9 mV11.6 mVPass
50% Load8.2 mV7.7 mV15.8 mV12.7 mVPass
60% Load9.3 mV7.4 mV15.7 mV15.0 mVPass
70% Load10.2 mV8.4 mV16.4 mV16.1 mVPass
80% Load11.1 mV8.1 mV18.4 mV16.8 mVPass
90% Load11.7 mV8.5 mV19.7 mV19.4 mVPass
100% Load19.2 mV10.9 mV21.8 mV23.6 mVPass
110% Load24.1 mV12.5 mV22.3 mV25.9 mVPass
Crossload 117.6 mV10.3 mV21.4 mV13.2 mVPass
Crossload 219.7 mV8.5 mV15.4 mV22.0 mVPass
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The ripple suppression is good overall here. At 3.3V and 5VSB we measure over 20mV under full load. That's not the best performance, but far from mediocre.

Ripple At Full Load

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Ripple At 110-Percent 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, whichcan cause problems in other close-by devices if too high.

We see some high EMI spikes here, with one exceeding the respective limit.

Things look better with the Peak EMI detector.

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