This application note describes the characteristics and performance of a 250 W wide range input and power factor corrected power supply designed to be used in an ATX application. Good electrical performance allows meeting the most demanding efficiency targets. The converter consists of four main blocks: (1) A PFC front-end stage using the L6563S PFC controller which generates the +400 V bus voltage. (2) An AHB (Asymmetrical half bridge) stage using the L6591 ZVS half bridge controller which performs the conversion from the high voltage bus to the +12 V output providing insulation. (3) Two DC-DC post-regulator stages using the L6727 which obtain the +5 V and +3.3 V outputs from the +12 V bus. (4) An auxiliary power supply (STANDBY) stage using the VIPer27H in isolated flyback configuration which provides the +5 V_SB output with 10 W power capability.