Abstract: A power supply apparatus which includes at least one switching power supply disposed in a chassis connected to earth ground and at least one D.C. to D.C. converter whose inputs float with respect to system ground. To reduce transmission of high-frequency electrical switching energy from the switching power supply to the load, the invention contemplates a tuned reactive circuit connected between the system ground and the earth ground. Electrical switching energy is shunted to earth ground by way of bypass capacitors located at various stages of the power supply apparatus. A further aspect of the apparatus contemplates the interposition of low-pass filters between the switching power supply and one or more D.C. to D.C. converters connected to the power supply and/or between the D.C. to D.C. converters and their respective loads to effectively eliminate radiated electromagnetic energy.