Power Supply Circuit and Adaptor

A power supply circuit, a power supply apparatus, and a control method are provided. The power supply circuit includes a primary unit, a modulating unit, a transformer, a secondary rectifier-filter unit, a voltage feedback unit, and a control unit. The control unit of the power supply circuit is configured to communicate with a device to-be-charged to adjust output power of the power supply circuit, to make at least one of output voltage and output current of the power supply circuit match a present charging stage of a battery of the device to-be-charged, and control the output voltage thereof within a first voltage range or a second voltage range.