A device for testing capacitive loads of a power supply includes a controller, a power supply switching circuit, a capacitive load switching circuit, and a current sampling circuit. The power supply switching circuit selects one of output voltages of the power supply to be electronically connected to the capacitive load switching circuit and the current sampling circuit. The current sampling circuit samples an output current of one output of the power supply selected by the controller. The controller turns on and off switches of the capacitive load switching circuit for matching an output current of the power supply with a reference current until the output current equals to the reference current. The controller outputs a total magnitude of the capacitive loads.