The magnet power supply system in ISIS particle accelerators was analyzed. On the ISIS synchrotron the dipoles, double quadrupoles and singlet quadrupoles magnets are connected in series using a configuration known 'White' circuit. The AC make up power supply is supplied to the primary of the White circuit via energy choke. The complete power supply is controlled via a digital STE bus control system. It avoids cumulative voltage across the magnets, which in the case of ISIS would result in a 140kV power system.