Why you can trust Tom's Hardware Our expert reviewers spend hours testing and comparing products and services so you can choose the best for you. Find out more about how we test.

Go to page:

Transient Response Tests, Timing 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 additional capacitance on the rails.

Advanced Transient Response at 20% – 20ms

Swipe to scroll horizontally

Voltage	Before	After	Change	Pass/Fail
12V	11.988V	11.710V	2.32%	Pass
5V	4.977V	4.864V	2.26%	Pass
3.3V	3.285V	3.118V	5.08%	Fail
5VSB	5.034V	4.983V	1.01%	Pass

Advanced Transient Response at 20% – 10ms

Swipe to scroll horizontally

Voltage	Before	After	Change	Pass/Fail
12V	11.986V	11.747V	1.99%	Pass
5V	4.977V	4.860V	2.35%	Pass
3.3V	3.285V	3.117V	5.11%	Fail
5VSB	5.034V	4.978V	1.11%	Pass

Advanced Transient Response at 20% – 1ms

Swipe to scroll horizontally

Voltage	Before	After	Change	Pass/Fail
12V	11.984V	11.720V	2.20%	Pass
5V	4.976V	4.867V	2.19%	Pass
3.3V	3.284V	3.120V	5.00%	Fail
5VSB	5.034V	4.983V	1.01%	Pass

Advanced Transient Response at 50% – 20ms

Swipe to scroll horizontally

Voltage	Before	After	Change	Pass/Fail
12V	11.953V	11.770V	1.53%	Pass
5V	4.973V	4.856V	2.36%	Pass
3.3V	3.281V	3.107V	5.31%	Fail
5VSB	5.019V	4.964V	1.10%	Pass

Advanced Transient Response at 50% – 10ms

Swipe to scroll horizontally

Voltage	Before	After	Change	Pass/Fail
12V	11.950V	11.792V	1.32%	Pass
5V	4.972V	4.851V	2.44%	Pass
3.3V	3.280V	3.106V	5.30%	Fail
5VSB	5.019V	4.966V	1.07%	Pass

Advanced Transient Response at 50% – 1ms

Swipe to scroll horizontally

Voltage	Before	After	Change	Pass/Fail
12V	11.948V	11.827V	1.01%	Pass
5V	4.972V	4.852V	2.42%	Pass
3.3V	3.279V	3.102V	5.39%	Fail
5VSB	5.019V	4.950V	1.37%	Pass

Image 1 of 8

Corsair TX550M — (Image credit: Tom's Hardware)

Transient response is not so tight at 12V. The 3.3V rail also performs terribly, failing in all tests. On the contrary, the 5V and 5VSB perform well 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.

Image 1 of 3

With only exception a small step at 5VSB, performance is good here.

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.

Swipe to scroll horizontally

PSU Timings Table
T1 (Power-on time) & T3 (PWR_OK delay)
Load	T1	T3
20%	39ms	127ms
100%	40ms	127ms

Image 1 of 4

PSU Timing Charts

The PWR_OK delay is within the 100-150ms region, so the PSU supports the alternative low power modes, 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).

Swipe to scroll horizontally

Test	12V	5V	3.3V	5VSB	Pass/Fail
10% Load	9.4 mV	6.2 mV	7.1 mV	15.7 mV	Pass
20% Load	19.3 mV	6.9 mV	8.7 mV	15.4 mV	Pass
30% Load	32.7 mV	12.3 mV	12.8 mV	15.6 mV	Pass
40% Load	27.6 mV	9.5 mV	10.6 mV	16.6 mV	Pass
50% Load	25.9 mV	11.6 mV	13.5 mV	18.0 mV	Pass
60% Load	24.9 mV	11.7 mV	14.2 mV	22.7 mV	Pass
70% Load	27.2 mV	12.8 mV	13.1 mV	20.6 mV	Pass
80% Load	25.4 mV	14.2 mV	17.2 mV	21.9 mV	Pass
90% Load	25.3 mV	13.5 mV	17.3 mV	21.7 mV	Pass
100% Load	40.3 mV	19.4 mV	21.1 mV	28.6 mV	Pass
110% Load	42.7 mV	21.5 mV	21.5 mV	29.4 mV	Pass
Crossload 1	15.8 mV	16.8 mV	17.0 mV	20.3 mV	Pass
Crossload 2	19.3 mV	14.1 mV	9.7 mV	18.6 mV	Pass
Crossload 3	12.5 mV	10.7 mV	18.0 mV	14.6 mV	Pass
Crossload 4	39.6 mV	15.0 mV	15.9 mV	21.2 mV	Pass

Image 1 of 4

With lower than 40mV ripple, the PSU would fare better against competing offerings. Not that 40mV is high in the worst-case scenario, but the bar is high in this section. Ripple at 5V and 3.3V is close to 20ms, which is low enough.

Ripple At Full Load

Image 1 of 4

Ripple At 110% Load

Image 1 of 4

Ripple At Cross-Load 1

Image 1 of 4

Ripple At Cross-Load 4

Image 1 of 4

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 cause increased static noise in your headphones or/and speakers.

΅We use TekBox's EMCview to conduct our EMC pre-compliance testing.