Advanced Transient Response Tests

In these tests, we monitor the response of the PSU in two different scenarios. First, a transient load (10 A at +12V, 5 A at 5V, 5 A at 3.3V, and 0.5 A at 5VSB) is applied to the PSU for 200 ms while the latter is working at 20% load. In the second scenario, the PSU, while working at 50% load, is hit by the same transient load. In both tests, we measure the voltage drops the transient load causes with our oscilloscope. Voltages should remain within the regulation limits defined by the ATX specification.

Real-world usage has a PSU always work with loads that change, depending on whether the CPU or graphics cards are busy. So it is of immense importance for the PSU to be able to keep its rails within the by the ATX specification defined ranges. The smaller the rail's deviations, the steadier the system will be, which results in less stress being put on its components.

We should note that the ATX specification requires for capacitive loading during transient tests, but in our methodology, we apply the worst case scenario with no extra capacitance on the rails. Although the ATX specification asks for this capacitance, your system (the mainboard and other parts) may not provide it, so we have to keep that scenario in mind as well.






In the 20% load transient response test, the +12V rail registers higher deviations than in the 50% test because the switching controller operates in PWM instead of FM mode. Registering well-controlled voltage drops throughout, the SF50 passes all tests successfully.

Below are the oscilloscope screenshots we took during Advanced Transient Response testing.

Transient Response at 20% Load

Transient Response at 50% Load

Turn-On Transient Tests

We measure the response of the PSU in simpler scenarios of transient load, during the power-on phase of the PSU, in the next set of tests. In the first test, we turn the PSU off, dial the maximum current 5VSB can output, and switch on the PSU. In the second test, we dial the maximum load +12V can handle and start the PSU while the PSU is in standby mode. In the last test, while the PSU is completely switched off (we cut off power or switch the PSU off by flipping its on/off switch), we dial the maximum load the +12V rail can handle before switching the PSU on from the loader and restoring power. The ATX specification states that recorded spikes on all rails should not exceed 10% of their nominal values (e.g., +10% for 12V is 13.2 V and 5.5 V for 5V).



No notable overshoots and spikes, just a few small waves in the last two tests, which are nothing to worry about.

Ripple Measurements

Ripple represents the AC fluctuations (periodic) and noise (random) in a PSU's DC rails. Ripple significantly decreases the lifespan of capacitors since it increases their temperature; a 10 °C increase can cut into a capacitor's life span by 50 percent. Ripple also plays an important role in overall system stability, especially when it is overclocked. The ripple limits, according to the ATX specification, are 120 mV (+12V) and 50 mV (5V, 3.3V, and 5VSB).


Very good ripple suppression on all rails without the use of in-line caps, which would make the cables bulky and difficult to work with.

Ripple at Full Load

Ripple at 110% Load

Ripple at Crossload 1

Ripple at Crossload 2