A power supply apparatus includes a coupling capacitor arranged to be connected on its first end to ground; a transformer including a primary winding and a secondary winding; a first rectifier bridge connected in parallel with the secondary winding; and an energy storage, to which a load is arranged to be connected. The primary winding is arranged to be connected between a second end of the coupling capacitor and a high voltage transmission line such that all current between the second end of the coupling capacitor and the high voltage transmission line passes through the primary winding. The energy storage is arranged to be charged by means of a current passing through the first rectifier bridge. Furthermore, the power supply apparatus includes a bypasser. A corresponding three-phase apparatus is also presented.