Hold-up TimeHold-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.
AC Loss To PWR_OK Hold-up Time
PWR_OK Inactive to DC Loss Delay
Hold-up time is close to 21 ms, which is much longer than what the ATX specification requires, and the power ok signal is accurate.
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 of 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.
|Timings for Alternative Sleep Mode|
|T0||AC power-on time||< 2s|
|T1||Power-on time||< 150 ms|
|T2||Rise time||0.2–20 ms|
|T3||PWR_OK delay||100–150 ms|
|T4||PWR_OK rise time||< 10 ms|
|T5||AC loss to PWR_OK hold-up time||> 16 ms|
|T6||PWR_OK inactive to DC loss delay||> 1 ms|
For the reviewed PSU, we measured T1 and T3 at 20% and 100% load.
|T1 (Power-on time) & T3 (PWR_OK delay)|
|20%||53 ms||134 ms|
|100%||53 ms||133 ms|
Power-on time is below 100 ms, and the PWR_OK delay is below 150 ms. This PSU supports Alternative Sleep Mode.