An adapter comprising: a power conversion unit, configured to convert an input alternating current to obtain an output voltage and an output current of the adapter, wherein the power conversion unit comprises a primary full-bridge rectification unit, a transformer, a secondary rectification unit, and a secondary filter unit, wherein the primary rectification unit is configured to directly output a voltage of a pulsating waveform without primary filter unit to the transformer; a voltage feedback unit, having an input end coupled to the power conversion unit, and configured to detect the output voltage of the adapter to generate a voltage feedback signal, the voltage feedback signal being configured to indicate whether the output voltage of the adapter reaches a set target voltage; a current feedback unit, having an input end coupled to the power conversion unit, and configured to detect the output current of the adapter to generate a current feedback signal, the current feedback signal being configured to indicate whether the output current of the adapter reaches a set target current; a power adjustment unit, having an input end coupled to an output end of the voltage feedback unit and to an output end of the current feedback unit, and an output end coupled to the power conversion unit, the power adjustment unit being configured to receive the voltage feedback signal and the current feedback signal and control the output voltage and the output current of the adapter to remain unchanged when the voltage feedback signal indicates the output voltage of the adapter has reached the set target voltage or when the current feedback signal indicates the output current of the adapter has reached the set target current; and a charging interface, having a data line configured to be used by the adapter to perform two-way communication with a device to be charged, and wherein the adapter is operable in a first charging mode which is a constant-voltage mode, and wherein in the constant-voltage mode, the target voltage is a voltage corresponding to the constant-voltage mode and the target current is the maximum current that the adapter is able to output under the constant-voltage mode; wherein the power adjustment unit is configured to adjust the output voltage of the adapter to the voltage corresponding to the constant-voltage mode based on the voltage feedback signal, and configured to control the output current of the adapter to not exceed the maximum current that the adapter is able to output in the constant-voltage mode when the current feedback signal indicates the output current of the adapter has reached the maximum current, wherein the output current of the adapter is a pulsating DC current. a power conversion unit, configured to convert an input alternating current to obtain an output voltage and an output current of the adapter, wherein the power conversion unit comprises a primary full-bridge rectification unit, a transformer, a secondary rectification unit, and a secondary filter unit, wherein the primary rectification unit is configured to directly output a voltage of a pulsating waveform without primary filter unit to the transformer; a voltage feedback unit, having an input end coupled to the power conversion unit, and configured to detect the output voltage of the adapter to generate a voltage feedback signal, the voltage feedback signal being configured to indicate whether the output voltage of the adapter reaches a set target voltage; a current feedback unit, having an input end coupled to the power conversion unit, and configured to detect the output current of the adapter to generate a current feedback signal, the current feedback signal being configured to indicate whether the output current of the adapter reaches a set target current; a power adjustment unit, having an input end coupled to an output end of the voltage feedback unit and to an output end of the current feedback unit, and an output end coupled to the power conversion unit, the power adjustment unit being configured to receive the voltage feedback signal and the current feedback signal and control the output voltage and the output current of the adapter to remain unchanged when the voltage feedback signal indicates the output voltage of the adapter has reached the set target voltage or when the current feedback signal indicates the output current of the adapter has reached the set target current; and a charging interface, having a data line configured to be used by the adapter to perform two-way communication with a device to be charged, and wherein the adapter is operable in a first charging mode which is a constant-voltage mode, and wherein in the constant-voltage mode, the target voltage is a voltage corresponding to the constant-voltage mode and the target current is the maximum current that the adapter is able to output under the constant-voltage mode; wherein the power adjustment unit is configured to adjust the output voltage of the adapter to the voltage corresponding to the constant-voltage mode based on the voltage feedback signal, and configured to control the output current of the adapter to not exceed the maximum current that the adapter is able to output in the constant-voltage mode when the current feedback signal indicates the output current of the adapter has reached the maximum current, wherein the output current of the adapter is a pulsating DC current.