An adapter, wherein the adapter supports a first charging mode and a second charging mode, a charging speed of the adapter charging a device to be charged in the second charging mode is greater than a charging speed of the adapter charging the device to be charged in the first charging mode, and the adapter comprises: 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 rectifier unit, a transformer, a secondary rectifier unit, and a secondary filter unit (211, 233) being coupled via switch transistor, the primary rectifier unit is configured as a half- or full-bridge rectifier to output a voltage with a pulsating waveform to the transformer directly; a voltage feedback unit, wherein an input end of the voltage feedback unit is coupled to the power conversion unit, and the voltage feedback unit is configured to detect the output voltage of the adapter to generate a voltage feedback signal, in which the voltage feedback signal is configured to indicate whether the output voltage of the adapter reaches a predetermined target voltage; a current feedback unit, wherein an input end of the current feedback unit is coupled to the power conversion unit, and the current feedback unit is configured to detect the output current of the adapter to generate a current feedback signal, wherein the current feedback signal is configured to indicate whether the output current of the adapter reaches a predetermined target current; a power adjusting unit, wherein an input end of the power adjusting unit is coupled to an output end of the voltage feedback unit and an output end of the current feedback unit respectively, an output end of the power adjusting unit is coupled to the power conversion unit, the power adjusting unit is configured to receive the voltage feedback signal and the current feedback signal, and to control the output voltage to remain constant when the voltage feedback signal indicates that the output voltage of the adapter reaches the target voltage; wherein in said first charging mode, the switch transistor is controlled to be on so that the secondary filter unit (211, 233) works so that to output a constant voltage, and wherein in said second charging mode, the switch transistor is controlled to be off so that the secondary filter unit (211, 233) does not work so that to output pulsating direct current and the output current of the adapter is controlled not to exceed the target current, by peak clipping the current greater than the target current; and a charging interface, wherein the adapter is configured to perform a bidirectional communication with the device to be charged via a data wire of the charging interface. 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 rectifier unit, a transformer, a secondary rectifier unit, and a secondary filter unit (211, 233) being coupled via switch transistor, the primary rectifier unit is configured as a half- or full-bridge rectifier to output a voltage with a pulsating waveform to the transformer directly; a voltage feedback unit, wherein an input end of the voltage feedback unit is coupled to the power conversion unit, and the voltage feedback unit is configured to detect the output voltage of the adapter to generate a voltage feedback signal, in which the voltage feedback signal is configured to indicate whether the output voltage of the adapter reaches a predetermined target voltage; a current feedback unit, wherein an input end of the current feedback unit is coupled to the power conversion unit, and the current feedback unit is configured to detect the output current of the adapter to generate a current feedback signal, wherein the current feedback signal is configured to indicate whether the output current of the adapter reaches a predetermined target current; a power adjusting unit, wherein an input end of the power adjusting unit is coupled to an output end of the voltage feedback unit and an output end of the current feedback unit respectively, an output end of the power adjusting unit is coupled to the power conversion unit, the power adjusting unit is configured to receive the voltage feedback signal and the current feedback signal, and to control the output voltage to remain constant when the voltage feedback signal indicates that the output voltage of the adapter reaches the target voltage; wherein in said first charging mode, the switch transistor is controlled to be on so that the secondary filter unit (211, 233) works so that to output a constant voltage, and wherein in said second charging mode, the switch transistor is controlled to be off so that the secondary filter unit (211, 233) does not work so that to output pulsating direct current and the output current of the adapter is controlled not to exceed the target current, by peak clipping the current greater than the target current; and a charging interface, wherein the adapter is configured to perform a bidirectional communication with the device to be charged via a data wire of the charging interface.