ATX12VO (12V Only) Desktop Power Supply
Design Guide
Power-On Time – REQUIRED
The power-on time is defined as the time from when PS_ON# is pulled low to when the +12 VDC output is within the regulation ranges specified in Table 4-2. The power-on time shall be less than 150 ms (T1 < 150 ms).
+12VSB shall have a power-on time of two second maximum after application of valid AC voltages as shown in the above figure. The 12VSB power on time is T0 as listed in Section 4.3.3.