Abstract: A power supply control system controls at least two variable power supplies feeding a common load connected to a common output terminal. A sensor monitors the current drawn by each power supply in dependence upon the difference detected in a sense to reduce the difference to zero. A summing circuit sums the outputs of all the comparators. Another comparator compares the output of the summing circuit with a zero level and produces an output to modify the reference signal. The loops comprising each comparator and the further comparator each act in a sense to reduce the output of the summing circuit to zero and in this way the system tends to maintain a balanced output from all supplies so that each supply shares the power requirement of the load according to its capacity while at the same time maintaining the output voltage at a level corresponding to the average of the nominal voltages of the individual supplies.