A power supply including a plurality of power supply modules and method of operating such a power supply includes monitoring the state of individual power supply modules. The power supply modules are monitored to prevent the operation of the modules outside a predetermined range. One power supply described herein includes a greater number of power supply modules than necessary to produce a desired output waveform. This allows a subset of power supply modules to be chosen to produce the desired output based on the state of each of the power supply modules as determined by monitoring.