A power supply device includes a PF correction circuit, a power switching circuit and a control circuit. The PF correction circuit converts an input voltage to a bus voltage according to a control signal to supply a later stage circuit. The power switching circuit selectively switches to conduct a first source or a second source to the PF correction circuit to provide the input voltage to the PF correction circuit. The control circuit outputs the control signal to the PF correction circuit. When the control circuit detects a first voltage of the first source connecting to the PF correction circuit is abnormal, the control circuit determines whether a second voltage of the second source is smaller than the bus voltage and controls the power switching circuit to switch when the second voltage is smaller than the bus voltage to conduct the second source to the PF correction circuit.