A multi-port power supply apparatus and its operation method are provided. The multi-port power supply apparatus includes a voltage source circuit, a first voltage converter, a second voltage converter and a first common control circuit. The voltage source circuit provides a source voltage. The first voltage converter converts the source voltage into a first output voltage and outputs the first output voltage to a first connecting port of the multi-port power supply apparatus. The second voltage converter converts the source voltage into a second output voltage and outputs the second output voltage to a second connecting port of the multi-port power supply apparatus. The first common control circuit adjusts the source voltage according to a first voltage demand of the first connecting port and a second voltage demand of the second connecting port. Thus, a voltage conversion efficiency of the multi-port power supply apparatus is enhanced.