Power supply capable of adjusting output voltage and operating system utilizing the same

A power supply capable of adjusting output voltage and providing power to a connector disposed on a motherboard is provided. The power supply includes a voltage generator, a first power path, a second power path, a detection circuit and a switching circuit. The voltage generator is configured to generate a first voltage, a second voltage, a third voltage and a fourth voltage. The first power path is configured to transmit the first voltage to a first pin of the connector. The second power path is configured to transmit the second voltage to a second pin of the connector. The detection circuit detects the voltage of a third pin of the connector to generate a detection signal. The switching circuit provides a third power path or a fourth power path according to the detection signal. The third power path is configured to transmit the third voltage to the third pin. The fourth power path is configured to transmit the four voltage to the third pin.