A high-voltage filter for an alternating-current (AC) to direct current (DC) power adapter of the type having a rectifier providing an internal ground and a high voltage DC, the high voltage DC coupled to drive a DC-DC converter providing a power adapter output, the high voltage filter coupled to filter the high voltage DC, has a first capacitor coupled between the high-voltage DC and an intermediate node. A second capacitor is coupled between the intermediate node and the internal ground. A source follower transistor has a drain coupled to the high-voltage and a source coupled to the intermediate node, with gate coupled to a reference supply. In a particular embodiment, the reference supply has a resistor coupled between the high voltage DC and the gate of the source follower, and at least one zener diode coupled between the gate of the source follower and internal ground.