Method and apparatus for detecting or suppressing electrical arcing or other abnormal change in the electrical impedance of a load connected to a power source. Preferably the load is a plasma chamber used for manufacturing electronic components such as semiconductors and flat panel displays. Arcing is detected by monitoring one or more sensors. Each sensor either responds to a characteristic of the electrical power being supplied by an electrical power source to the plasma or is coupled to the plasma chamber so as to respond to an electromagnetic condition within the chamber. Arcing is suppressed by reducing the power output for a brief period. Then the power source increases its power output, preferably to its original value. If the arcing resumes, the power source repeats the steps of reducing and then restoring the power output.