Hold Up Time

Hold up time represents the duration a PSU can maintain stable output as defined by the ATX specification without input power. This is very important when the quality of your electricity varies, and there are short drops in the supply (dips or brownouts).

In the oscilloscope screenshots below, the blue line is the AC input mains signal, the green line the "Power Good" signal, and the yellow line the +12V rail. The measured timing variable is listed as ΔX.

Hold Up Time

AC Loss To PWR_OK Hold Up Time

PWR_OK Inactive to DC Loss Delay

Hold-up time is long enough, and the power ok signal is accurate, so everything is fine.

Timings for Alternative Sleep Mode (ASM)

Traditionally, sleep mode (S3) shuts the system off for a long time (minutes or hours) to reduce power consumption. However, this approach adds a few seconds delay when resuming from standby. Microsoft recently introduced Modern Sleep, which brings the instant-on capability to PCs—just like your phone instantly turns on, without any noticeable delay. Modern Sleep builds on the Alternative Sleep Mode capability, which Intel has defined. To support ASM, a power supply must wake up from sleep quickly, to ensure system stability, think of it as the PSU's boot time.


For the reviewed PSU, we measured T1 and T3 at 20% and 100% load.



The PWR_OK delay sits inside the 100–150 ms window, so the PSU is compatible with alternative sleep mode.