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% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.054V | 11.618V | 3.62% | Pass |
| 5V | 5.105V | 4.899V | 4.04% | Pass |
| 3.3V | 3.324V | 3.126V | 5.95% | Fail |
| 5VSB | 5.091V | 5.011V | 1.57% | Pass |
Advanced Transient Response at 20% – 10ms
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.059V | 11.599V | 3.81% | Pass |
| 5V | 5.108V | 4.903V | 4.02% | Pass |
| 3.3V | 3.325V | 3.128V | 5.92% | Fail |
| 5VSB | 5.090V | 5.014V | 1.50% | Pass |
Advanced Transient Response at 20% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.068V | 11.629V | 3.64% | Pass |
| 5V | 5.113V | 4.906V | 4.04% | Pass |
| 3.3V | 3.327V | 3.109V | 6.56% | Fail |
| 5VSB | 5.090V | 4.998V | 1.81% | Pass |
Advanced Transient Response at 50% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.011V | 11.756V | 2.12% | Pass |
| 5V | 5.100V | 4.924V | 3.45% | Pass |
| 3.3V | 3.319V | 3.112V | 6.22% | Fail |
| 5VSB | 5.076V | 5.002V | 1.46% | Pass |
Advanced Transient Response at 50% – 10ms
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.023V | 11.746V | 2.30% | Pass |
| 5V | 5.106V | 4.894V | 4.16% | Pass |
| 3.3V | 3.321V | 3.117V | 6.15% | Fail |
| 5VSB | 5.075V | 4.991V | 1.66% | Pass |
Advanced Transient Response at 50% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.023V | 11.759V | 2.19% | Pass |
| 5V | 5.105V | 4.932V | 3.39% | Pass |
| 3.3V | 3.321V | 3.115V | 6.21% | Fail |
| 5VSB | 5.075V | 4.981V | 1.84% | Pass |
Transient response is mediocre on all rails but 5VSB, where it doesn't matter so much.
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.
There is a huge voltage drop in the "PSU OFF To Full 12V" test, showing that something is off with the resonant controller's programming.
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.
| T1 (Power-on time) & T3 (PWR_OK delay) | ||
|---|---|---|
| Load | T1 | T3 |
| 20% | 36ms | 129ms |
| 100% | 36ms | 128ms |
The PWR_OK delay is within the 100-150ms region, so the PSU supports the alternative sleep mode 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).
| Test | 12V | 5V | 3.3V | 5VSB | Pass/Fail |
| 10% Load | 53.0 mV | 11.1 mV | 9.0 mV | 40.1 mV | Pass |
| 20% Load | 30.5 mV | 8.3 mV | 8.8 mV | 12.5 mV | Pass |
| 30% Load | 24.4 mV | 9.8 mV | 9.0 mV | 17.2 mV | Pass |
| 40% Load | 45.0 mV | 11.4 mV | 9.8 mV | 36.7 mV | Pass |
| 50% Load | 40.9 mV | 13.5 mV | 10.7 mV | 42.1 mV | Pass |
| 60% Load | 36.0 mV | 14.2 mV | 10.4 mV | 37.7 mV | Pass |
| 70% Load | 41.2 mV | 13.6 mV | 10.9 mV | 40.0 mV | Pass |
| 80% Load | 20.9 mV | 13.2 mV | 12.7 mV | 23.0 mV | Pass |
| 90% Load | 39.0 mV | 15.3 mV | 13.0 mV | 44.4 mV | Pass |
| 100% Load | 33.3 mV | 19.6 mV | 15.7 mV | 31.9 mV | Pass |
| 110% Load | 38.8 mV | 18.5 mV | 16.1 mV | 32.5 mV | Pass |
| Crossload 1 | 33.5 mV | 16.2 mV | 15.6 mV | 14.1 mV | Pass |
| Crossload 2 | 27.8 mV | 12.9 mV | 8.9 mV | 11.7 mV | Pass |
| Crossload 3 | 44.7 mV | 10.4 mV | 16.8 mV | 34.9 mV | Pass |
| Crossload 4 | 32.5 mV | 15.6 mV | 12.1 mV | 25.2 mV | Pass |
Ripple suppression is good on all major rails. The 5VSB needs a better filtering cap.
Ripple At Full Load
Ripple At 110% Load
Ripple At Cross-Load 1
Ripple At Cross-Load 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.
A single spur exceeds the limits of the average and peak EMI detectors. Conducted EMI is low in all other frequencies.
MORE: Best Power Supplies
MORE: How We Test Power Supplies
MORE: All Power Supply Content
DaMAgeCard SD Express card vulnerability leverages the privileged access that PCIe provides — bypasses traditional software-based security mechanisms
Raspberry Pi Monitor Review: Well-built portable monitor that works with any HDMI-capable device
Raspberry Pi 500 Review: The keyboard is the computer, again
