Abstract: Voltage in a transfer arc power supply of a plasma jet cleaning apparatus employed to induce a cathode workpiece current for cleaning a surface of the workpiece includes apparatus for cyclically varying the applied voltage between at least two negative levels which are effective to induce two levels of workpiece current. The more negative voltage is effective to produce a large workpiece current and to clean dielectric impurities from the surface of the workpiece. The less negative voltage is effective to maintain current flow but to permit enhanced motion of the plasma jet over the workpiece surface so that any tendency for sticking of cathode spots on the workpiece during existence of the more negative voltage is counteracted.