PS-ON Signal explained

PS-ON Signal is a pin on a 20-pin or 24-pin ATX-specified power connector used to turn a personal computer power supply unit on/off. The PS_ON pin is normally pulled high in an open-circuit, but will turn on the power supply when it is pulled low, by shorting it to the common signal (COM). Conversely the power supply is turned off when the PS-ON is in open-circuit. ^{[1] [2]}

The PS_ON pin can be jumpered to manually turn a PSU on.^[3]

Notes and References

1. Web site: SG6516 PC Power Supply Supervisors. Fairchild Semiconductor. https://web.archive.org/web/20180821093928/https://www.fairchildsemi.com/datasheets/SG/SG6516.pdf. August 21, 2018. 2018-08-21.
2. Web site: Desktop Platform Form Factors Power Supply Design Guide. Intel Corporation. August 21, 2018.
3. Web site: How to Jump a PSU bit-tech.net . 2023-12-11 . bit-tech.net . en.