Power supply system with low power standby supply for control unit

A power supply system (100) includes: a switching power supply (21, 20), which rectifies and smoothes an AC voltage of an AC power supply to generate a first DC voltage in a normal mode; a control unit (51), which controls the switching power supply to switch between the normal mode and a power saving mode; and a low-capacity power supply circuit, which supplies power to the control unit in the power saving mode, and which includes: a first capacitor (C1), which includes a first electrode connected to one end of the AC power supply, and a second electrode; a second capacitor (C2), which includes a first electrode connected to the other end of the AC power supply, and a second electrode; a rectifying circuit (31), which rectify an AC voltage applied to both capacitors; and a smoothing circuit (32), which smoothes the rectified AC voltage to generate a smooth voltage.