Abstract: A power supply system generates a.c. power which is applied through a high voltage transformer to the electrodes of a treater. It includes a converter circuit which transforms a.c. electric power to d.c. power and an inverter which transforms the d.c. power to a.c. power. A feedback circuit senses the power delivered to the treater and separate control of both inverter frequency and output voltage is employed to prevent arc-over during the treatment process. The power supply system is particularly responsive to sudden changes in the operating conditions, and this enables treatment of relatively thin materials on a bare metal roller.