A converter and a power supply system are disclosed, and relate to the power electronics field, to resolve a problem that a sampling circuit in an OBC circuit is relatively complex. The converter includes an alternating current unit, a switching unit, a conversion unit, a direct current unit, and a controller. The alternating current unit includes a U line, a V line, a W line, and an N line. The N line is connected to a ground of the controller, so that the controller can be directly connected to the U line, the V line, and the W line, to collect a voltage of the U line, a voltage of the V line, and a voltage of the W line. This simplifies the sampling circuit.