A power supply circuit includes a voltage converting module, a detecting module, a processor, and a selecting module. The voltage converting module includes at least one output port, each of which is connected to one load circuit to form a loop circuit. The detecting module can be selectively connected to a selected one of the formed loop circuits to detect at least one parameter of the loop circuit. The processor controls the selecting module to connect the detecting module to the selected loop circuit, and further determines the current of the loop circuit according to the at least one parameter.