An in-rush current controller to turn-on a semiconductor output switch is described. The output switch is arranged in series with an output capacitor. The switch comprises a switch control port for controlling an output current and an output voltage. The controller comprises an amplifier to source or sink a switch control current to or from the switch control port, wherein the switch control current is dependent on an amplifier control current at an amplifier control port. The controller comprises a reference current source to provide a reference current at the amplifier control port, subject to a control signal indicating that the output switch is to be turned on. Furthermore, the controller comprises a feedback capacitor to provide a feedback current at the amplifier control port in dependence of a variation of the output voltage.