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.
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 | 12.085V | 11.998V | 0.72% | Pass |
| 5V | 4.996V | 4.903V | 1.86% | Pass |
| 3.3V | 3.325V | 3.195V | 3.91% | Pass |
| 5VSB | 5.069V | 5.013V | 1.10% | Pass |
Advanced Transient Response at 20% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.085V | 11.958V | 1.05% | Pass |
| 5V | 4.996V | 4.884V | 2.24% | Pass |
| 3.3V | 3.325V | 3.169V | 4.69% | Pass |
| 5VSB | 5.069V | 5.018V | 1.01% | Pass |
Advanced Transient Response at 20% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.085V | 11.975V | 0.91% | Pass |
| 5V | 4.996V | 4.885V | 2.22% | Pass |
| 3.3V | 3.325V | 3.165V | 4.81% | Pass |
| 5VSB | 5.069V | 5.019V | 0.99% | Pass |
Advanced Transient Response at 50% – 200ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.078V | 12.003V | 0.62% | Pass |
| 5V | 4.991V | 4.892V | 1.98% | Pass |
| 3.3V | 3.319V | 3.182V | 4.13% | Pass |
| 5VSB | 5.035V | 4.977V | 1.15% | Pass |
Advanced Transient Response at 50% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.077V | 11.952V | 1.04% | Pass |
| 5V | 4.991V | 4.875V | 2.32% | Pass |
| 3.3V | 3.319V | 3.157V | 4.88% | Pass |
| 5VSB | 5.035V | 5.000V | 0.70% | Pass |
Advanced Transient Response at 50% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.077V | 11.967V | 0.91% | Pass |
| 5V | 4.991V | 4.875V | 2.32% | Pass |
| 3.3V | 3.320V | 3.156V | 4.94% | Pass |
| 5VSB | 5.034V | 4.986V | 0.95% | Pass |
The transient response of the +12V rail, which is the most important, is excellent, and the same goes for 5VSB. The 5V rail has satisfactory performance, while there is room for improvement at 3.3V, where the voltage level dropped below 3.2V, in all 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.
Typically for a Seasonic Focus-based platform, the +12V rail requires some time till it reaches the nominal voltage. There is nothing to worry about, though.
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.
| T1 (Power-on time) & T3 (PWR_OK delay) | ||
|---|---|---|
| Load | T1 | T3 |
| 20% | 82ms | 318ms |
| 50% | 100ms | 318ms |
The PWR_OK delay is out of the 100-150ms region, so the PSU does not support the alternative sleep mode, which is a requirement by the newest ATX spec.
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 | 11.8 mV | 8.6 mV | 12.7 mV | 6.1 mV | Pass |
| 20% Load | 15.4 mV | 9.6 mV | 14.7 mV | 6.2 mV | Pass |
| 30% Load | 17.3 mV | 10.4 mV | 16.0 mV | 6.8 mV | Pass |
| 40% Load | 19.5 mV | 11.6 mV | 18.2 mV | 7.5 mV | Pass |
| 50% Load | 19.9 mV | 11.2 mV | 19.8 mV | 7.8 mV | Pass |
| 60% Load | 16.9 mV | 11.1 mV | 22.0 mV | 9.4 mV | Pass |
| 70% Load | 15.9 mV | 11.5 mV | 22.5 mV | 10.4 mV | Pass |
| 80% Load | 16.5 mV | 11.5 mV | 17.5 mV | 11.4 mV | Pass |
| 90% Load | 17.9 mV | 11.8 mV | 17.9 mV | 13.0 mV | Pass |
| 100% Load | 29.1 mV | 12.8 mV | 20.3 mV | 14.2 mV | Pass |
| 110% Load | 32.3 mV | 12.9 mV | 22.3 mV | 14.4 mV | Pass |
| Crossload 1 | 18.6 mV | 11.5 mV | 19.1 mV | 6.8 mV | Pass |
| Crossload 2 | 28.5 mV | 10.8 mV | 20.0 mV | 12.3 mV | Pass |
The ripple at +12V with full load increases significantly, still it remains below 30mV. All in all, the ripple suppression is good on all rails, but nowhere close to the amazing levels that the Corsair RM750x model achieves, thanks to the good design and the in-cable caps.
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.
Two high spurs exceed the limits with the average and the QP detectors, at 342KHz and 581KHz, respectively.
MORE: Best Power Supplies
MORE: How We Test Power Supplies
MORE: All Power Supply Content
