A power supply device includes a power supply circuit, a detection circuit, and a control circuit. The power supply circuit is configured to output a supply voltage. The detection circuit is configured to sequentially provide a first predetermined resistance and a second predetermined resistance according to a plurality of switching signals, in order to operate with an electronic device and the supply voltage to sequentially obtain a first detection voltage and a second detection voltage. The control circuit is configured to generate the switching signals, and determine a load resistance of the electronic device according to the first detection voltage and the second detection voltage. The control circuit is further configured to determine whether the load resistance is within a predetermined resistance range, and the power supply circuit is further configured to drive the electronic device if the load resistance is within the predetermined resistance range.