A power supply system includes a power distribution branch, a charging branch, and a control unit. The power distribution branch receives a first current. The charging branch includes a charging unit, and the charging branch receives a second current to charge an electric vehicle through the charging unit. The control unit is connected to the charging unit, and receives a current signal of the first current consumed by the power distribution branch. The control unit calculates an adjustment value of the second current according to a variation value of the first current when the first current is varied. A sum of the first current and the second current is less than or equal to an upper-limit value of a total household current. The control unit produces a charging command according to the adjustment value of the second current and provides the charging command to the charging unit.