Switching power supplies can be categorized as AC-DC power supplies (AC input) and DC-DC converters (DC input) since both incorporate DC to AC conversion for voltage change. By virtue of the inherent design characteristics, switching power supplies generate electromagnetic interference composed of signals of multiple frequencies. The DC-DC converter converts the input DC voltage to an AC voltage that can be stepped up or down via a transformer. AC-DC power supplies also utilize high frequency circuits for voltage conversion. However, the internal AC voltage in either case is not a pure sine wave but frequently a square wave which can be represented by a Fourier series that consists of the algebraic sum of many sine waves with harmonically-related frequencies. These multiple-frequency signals are the source of conducted and radiated emissions which can cause interference to both the equipment in which the switching power supply is installed and to nearby equipment which may be susceptible to these frequencies.