Abstract: A power supply apparatus includes a full-wave rectifying circuit for converting an AC input voltage to a rectified voltage and a controller coupled to the full-wave rectifying circuit. The full-wave rectifying circuit includes a first switching circuit and a second switching circuit. During a general stage, the controller controls the first or second switching circuit to perform an active rectifying operation once an absolute value of the AC input voltage is greater than a lower bound voltage. During an initialization stage, the full-wave rectifying circuit performs a passive rectifying operation to convert the AC input voltage to the rectified voltage, and the controller controls the first or second switching circuit to switch from performing the passive rectifying operation to performing the active rectifying operation once the absolute value of the AC input voltage reaches or exceeds an upper bound voltage.