Hold-Up Time

Hold-up time represents the duration which a PSU can maintain stable output as defined by the ATX specification without input power. This rating becomes 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 is the "Power Good" signal, and the yellow line is 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 might not reach the ATX spec's requirements, but it is notably longer than the SF750 Platinum and SP750 high-end units. The restricted space on the PCB doesn't allow for large enough bulk caps in the majority of SFX platforms.

Timings for Alternative Low Power Modes (ALPM)

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

I measured T1 and T3 at 20% and 100% load for the reviewed PSU.



Power-on time is below 50 ms, which is good. PWR_OK delay is in the 100-150 ms range, so the PSU supports Alternative Low Power Modes.