An alternating-current (AC)—direct-current (DC) power supply includes a circuit board including an alternating-current input terminal to which an alternating current is input and a direct-current output terminal from which a direct current is output. The AC-DC power supply includes a diode bridge that rectifies the alternating current input via the alternating-current input terminal, an alternating-current input line that electrically connects the alternating-current input terminal and the diode bridge, a coil connected to the diode bridge, a diode connected to the direct-current output terminal, a switching line that electrically connects the coil and the diode, and a switching element connected to the switching line. A portion of the switching line is disposed at right angles to a portion of the alternating-current input line.