This power-supply device (1) is provided with: a rectifier (51 or 52), the respective input terminals of which are connected to one end of each of a number of switching elements (41 or 42) that perform synchronous rectification; a coil (43), one end of which is connected to an output end of this power-supply device (1); and a second capacitor (53) that is connected in series with a first capacitor (44). One end of said first capacitor (44) is grounded, one end of the second capacitor (53) is connected to a point where the other end of the first capacitor (44) is connected to the aforementioned one end of the coil (43), and the other end of the second capacitor (53) is connected to the output terminals of the rectifier (51 or 52).