Abstract: A power supply device includes a power supply unit that outputs alternating current, an output unit connectable to a power supply line, and an adjusting unit that adjusts the capacitance of a power supply circuit between the power supply unit and the output unit. The adjusting unit includes a first capacitor, a second capacitor, and a circuit switching mechanism. The circuit switching mechanism can switch between a series connection state in which the first capacitor and the second capacitor are connected in series between the power supply unit and the output unit, and a parallel connection state in which the first capacitor and the second capacitor are connected in parallel between the power supply unit and the output unit.