Power supply device and abnormality determination method for A/D converter

A power supply device includes a voltage adjusting unit, an A/D converter, a determination unit, and a supply unit configured to supply a voltage. The A/D converter includes an A/D conversion circuit, and a selector that connects any one of a plurality of input ports to the A/D conversion circuit. The input ports include load ports, a first diagnostic port, and a second diagnostic port, the supply unit supplies a first voltage value to the first diagnostic port and supplies a second voltage value to the second diagnostic port, and the determination unit determines abnormality of the A/D converter on the basis of conversion results by the A/D conversion circuit when the first diagnostic port and the A/D conversion circuit are connected together and conversion results by the A/D conversion circuit when the second diagnostic port and the A/D conversion circuit are connected together.