A power supply system for an AC type of coalescer including a first transformer, a controllable transformer, a resonant control circuit and a control system. The first transformer has a primary winding with first and second primary terminals and a secondary winding with first and second secondary terminals, where the first and second secondary terminals are provided for connection to electrodes of the coalescer. The controllable transformer has a primary side for connection to an AC power source and a secondary side connected to first and second nodes, where the second node is connected to a second primary terminal of the first transformer. The resonant control circuit is connected between the first node and the second node. The control system is controlling the controllable transformer. The power supply system further comprises a capacitor connected between the first node and a first primary terminal of the first transformer.