A power supply device includes a substrate, a transformer, a rectifying section, a filtering section, at least one first capacitor section, and a second capacitor section. The substrate includes at least one semiconductor element. The transformer inputs an electric power via at least one pair of primary-side terminals, transforms the input electric power, and outputs the transformed electric power via at least one pair of secondary-side terminals. The rectifying section includes at least one rectifying element configured to rectify the transformed electric power. The filtering section reduces alternating-current components included in the rectified electric power. The first capacitor section is connected in parallel to the at least one rectifying element. The second capacitor section generates one or more harmonic waves that reduce a peak value of a fundamental wave of resonance generated based on a leakage inductance component of the transformer and a capacitance component of the first capacitor section.
