Abstract: A d.c. power supply system comprises a plurality of voltage regulating power supplies connected in a master slave configuration, the number of regulators being one greater than required to provide load current requirements. The master regulator generates a control signal to control the output of the individual slave regulators to provide balanced load sharing. Failure of one of the slave regulators is detected and the failed regulator replaced by the redundant regulator without interference to the output load current. Failure of the master regulator is detected by steering circuitry within each slave which senses an improper master error signal and transfers control to the reference error amplifier circuity of the slave regulators. Diagnosis of the error conditions is provided by logical analysis of output currents.