The design of three switched mode power supplies based on flyback dc-dc converter with different power 20,24 and 6 Watt and output voltage 5,12 and -12 respectively is achieved. The designed power stage is based on the bipolar transistor as the main switching device with protection network used to ensure safe operation. The microprocessor and its supervisor board are used with slight software program to control the output of the multi-switched mode power supplies even though they have different operating switching frequency, output voltage, output power. The system performance is simulated and examined under many desired operation conditions. From the obtained results it was found that, it is efficiently and easily to use the microprocessor to control multi- switched mode power supplies reducing the complexity of the system.