A power controller includes a signal identification element including a low-frequency signal identifier, a switch driver, a switch element. The low-frequency signal identifier includes a comparator, a rising-edge trigger, a falling-edge trigger, a counting unit, and a latch. The comparator receives a second input signal and compares the second input signal with a first reference voltage to generate a comparison signal. The rising-edge trigger and the falling-edge trigger receive the comparison signal. The counting unit includes a counting element and an OR gate. The OR gate generates a logic signal according to the outputs of the rising-edge trigger and the falling-edge trigger, and the counting element generates a count output signal accordingly. The latch determines whether the second input signal is a direct-current signal or a power-frequency signal according to the logic signal and the count output signal l, thereby controlling the switch driver to operate the switch element.