A power supply system includes a power control device and a power supply device. The power control device includes a first controller, a power measurement circuit, and a first communication circuit. The power measurement circuit measures power being supplied to the power supply device. The first controller calculates additionally suppliable power based on the power being supplied and selects one operation mode based on the additionally suppliable power. The first communication circuit transmits the operation mode selected to the power supply device. The power supply device includes a second controller, a power converter circuit, and a second communication circuit. The second communication circuit receives the operation mode selected. The second controller outputs a condition of supply power indicating electric power supplied, to the power converter circuit. The power converter circuit converts electric power based on the condition of supply power, and supplies the electric power converted to an external device.