POWER SOURCE DEVICE

A power supply device for supplying power to a load by combining a secondary battery and a capacitor includes a bypass switch which enables power to be directly supplied to the load from the capacitor by being switched to a connected state when a voltage of the capacitor is a voltage capable of driving the load, and a first DC-DC converter which enables the voltage of the capacitor to be stepped up and supplied to the load when the voltage of the capacitor drops below a minimum voltage capable of driving the load.