A power supply apparatus that suppresses radiation of noise while supplying a stable voltage, and a method of supplying power are provided. The power supply apparatus includes a power conversion unit configured to input a voltage to convert the voltage into an electric power; and a smoothing unit configured to include a coil, a capacitor, and a cable in which power supply wires connecting one end of the capacitor to the coil and ground wires connecting the other end of the capacitor to a ground of the power conversion unit are alternately arranged, and to smooth the voltage output from the power conversion unit.