This article will discuss about the alert function of pc power supply. The main voltage power supply, which supply the computer is +12 volts. Power supply for this circuit should provide a large output current, especially in computers with lots of drive bays. 12 V is applied also to the fans, who tend to work all the time. Usually, the fan motor consumes between 100 and 250 mA, but with newer computers, this value is less than 100 mA.