Control (power on/off, monitor) a desktop PC with ESP8266?
PC Power switch is a logic switch to Gnd with standby +5V R_pullup on the switch. It is a toggle function so just momentary using NPN open collector to 0V.  The base drive current is amplified so only needs&lt; 0.1mA so +5Vstdby can provide this. 9V is redundant.