Abstract: A switching AC/DC power supply system with a 10 MHz time base includes a master and at least one slave, each of which has a time base generator, and the time base generators can provide a time base of 10 MHz. Wherein the slave has a selector switch, and when the master is coupled to the slave, the slave can obtain the time base from the time base generator of the master through the selector switch, thereby enabling the time base of the slave is fully synchronized with the master and improving the power output quality of the switching AC/DC power supply system.