The present invention relates to the photoelectric field, and provides a power supply system and a power supply method, so as to reduce costs of a lead between a positive electrode or a negative electrode of a photovoltaic panel and a direct current voltage source. The power supply system includes: a photovoltaic panel string, an inverter connected to the photovoltaic panel string, and a transformer connected to the inverter. The power supply system further includes a voltage controller. The voltage controller includes a first terminal, a second terminal, and a third terminal. The voltage controller further includes: a first sampling unit, a control unit connected to the first sampling unit, and an inverter unit.