A PSU that processes electric power from AC line without using line frequency transformer. Such supply can still be isolating if it uses high-frequency transformer in one of its power conversion stages. A typical off-line SMPS rectifies input AC line voltage, produces high-frequency pulses by using semiconductor power switches, changes the voltage level by using inductors and/or transformers, then rectifies it again and filters for DC output. An example of isolating off-line PSU is a switching power supply of a computer.