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.
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% – 200ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.003V | 11.926V | 0.64% | Pass |
| 5V | 5.081V | 5.017V | 1.26% | Pass |
| 3.3V | 3.293V | 3.190V | 3.13% | Pass |
| 5VSB | 5.067V | 5.016V | 1.01% | Pass |
Advanced Transient Response at 20% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.998V | 11.890V | 0.90% | Pass |
| 5V | 5.081V | 5.007V | 1.46% | Pass |
| 3.3V | 3.293V | 3.171V | 3.70% | Pass |
| 5VSB | 5.067V | 5.014V | 1.05% | Pass |
Advanced Transient Response at 20% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.000V | 11.907V | 0.78% | Pass |
| 5V | 5.081V | 5.004V | 1.52% | Pass |
| 3.3V | 3.293V | 3.164V | 3.92% | Pass |
| 5VSB | 5.067V | 5.013V | 1.07% | Pass |
Advanced Transient Response at 50% – 200ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.993V | 11.915V | 0.65% | Pass |
| 5V | 5.070V | 5.002V | 1.34% | Pass |
| 3.3V | 3.285V | 3.175V | 3.35% | Pass |
| 5VSB | 5.050V | 5.001V | 0.97% | Pass |
Advanced Transient Response at 50% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.996V | 11.894V | 0.85% | Pass |
| 5V | 5.070V | 4.987V | 1.64% | Pass |
| 3.3V | 3.285V | 3.155V | 3.96% | Pass |
| 5VSB | 5.050V | 4.998V | 1.03% | Pass |
Advanced Transient Response at 50% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.001V | 11.903V | 0.82% | Pass |
| 5V | 5.069V | 4.984V | 1.68% | Pass |
| 3.3V | 3.285V | 3.152V | 4.05% | Pass |
| 5VSB | 5.049V | 4.989V | 1.19% | Pass |
The transient response is very good at +12V, which is the most important rail. In the rest rails, the deviations are also low, but the voltage levels at 3.3V drop lower than 3.2V once the transient load is applied, because of the low nominal (initial) voltage.
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.
The turn-on transient slopes are almost perfect. There is only a tiny spike at 5VSB, which cannot spoil of course the overall picture.
Ripple Measurements
Ripple represent 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).
| Test | 12V | 5V | 3.3V | 5VSB | Pass/Fail |
| 10% Load | 6.0 mV | 4.4 mV | 11.8 mV | 7.2 mV | Pass |
| 20% Load | 7.8 mV | 4.8 mV | 12.6 mV | 7.6 mV | Pass |
| 30% Load | 9.6 mV | 5.6 mV | 13.8 mV | 12.4 mV | Pass |
| 40% Load | 9.8 mV | 6.8 mV | 15.6 mV | 9.2 mV | Pass |
| 50% Load | 9.8 mV | 10.5 mV | 18.4 mV | 11.0 mV | Pass |
| 60% Load | 11.0 mV | 8.3 mV | 17.7 mV | 10.3 mV | Pass |
| 70% Load | 13.6 mV | 11.6 mV | 19.6 mV | 12.6 mV | Pass |
| 80% Load | 15.5 mV | 19.4 mV | 26.0 mV | 18.5 mV | Pass |
| 90% Load | 18.2 mV | 15.1 mV | 23.0 mV | 13.4 mV | Pass |
| 100% Load | 23.3 mV | 13.6 mV | 25.0 mV | 14.7 mV | Pass |
| 110% Load | 26.4 mV | 14.5 mV | 27.8 mV | 16.2 mV | Pass |
| Crossload 1 | 9.7 mV | 5.4 mV | 21.9 mV | 8.1 mV | Pass |
| Crossload 2 | 25.9 mV | 12.8 mV | 28.2 mV | 15.8 mV | Pass |
The ripple suppression is satisfactory. It could be a little better, though, at 3.3V, but this rail isn't heavily used nowadays.
Ripple At Full Load
Ripple At 110% Load
Ripple At Cross-Load 1
Ripple At Cross-Load 2
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 increased at low frequencies. Still, none of them exceeds the limits.
MORE: Best Power Supplies
MORE: How We Test Power Supplies
MORE: All Power Supply Content
Nintendo Switch 2 design seemingly leaked by carrying case maker — similar aesthetics but with a larger screen and Joy-Cons
Elon Musk reportedly wanted OpenAI to be a for-profit entity but has now sued to block the move
PlayStation 5 transformed into a laptop for $2,750 — Chinese modders made Sony's console more portable with a 17.3-inch 4K display weighing over 9 pounds
