According to one embodiment, a power supply device includes a rectifying circuit configured to rectify an alternating-current power supply, a first capacitor configured to smooth a voltage after rectification, and a falling voltage chopper circuit configured to supply electric power to a load. The first capacitor is set to a capacity in which a section where a voltage after smoothing drops to an output voltage to the load is provided in a rectified half period of the alternating-current power supply. The falling voltage chopper circuit includes at least one switching element configured to receive an input of the voltage after smoothing, operate in a section where the voltage after smoothing exceeds the output voltage, and pause in a section of the output voltage and a second capacitor provided on an output side and having a capacity larger than the capacity of the first capacitor.