A power supply apparatus having multiple output ports includes: a master power supply circuit for supplying a master output power via a master power switch; a slave power supply circuit for supplying a slave output power via a slave power switch; and a shared resistor coupled between a power management node and a reference ground level. The slave sensing circuit outputs the slave sensing current via a slave power management pin, to generate a total power signal at the power management node. The master control circuit senses the total power signal via the master power management pin, to determine an adjustment current. The slave control circuit controls the slave power switch according to a voltage at the slave power management pin, to adjust the slave output power, so that a total power of the master output power and the slave output power does not exceed a predetermined power range.