A power supply includes a power supply module, a microcontroller, a setting unit, a number of switch units, a number of current detection units, and a number of output connectors. Each switch unit is connected to one output connector via one current detection unit. The power supply module converts an alternating current (AC) voltage into a direct current (DC) to power electronic devices connected to each output connector by the corresponding switch unit, and the corresponding current detection unit. Each current detection unit detects a current passing through the output connector. The microcontroller calculates a total power of the power supply module according the detected currents and the DC voltage, and turns off all the switch units when the total power is greater than a predetermined current according to a protection mode set in the setting unit.