An adapter, being operable in a first charging mode and a second charging mode, wherein a charging speed of a device to be charged by the adapter in the second charging mode is faster than in the first charging mode, the adapter comprising: a power conversion unit, configured to convert an input alternating current, AC, to obtain an output voltage and an output current of the adapter, wherein the output current of the adapter is a current of a first pulsating waveform, and wherein the power conversion unit comprises an AC input end, a primary rectification unit, a transformer, a secondary rectification unit, and a first rectification unit, the primary rectification unit being configured to transfer a pulsating direct current without primary filtering unit to the transformer; a sample and hold unit, connected to the power conversion unit, and configured to sample the current of the first pulsating waveform when the sample and hold unit is in a sampling state and hold a peak value of the current of the first pulsating waveform when the sample and hold unit is in a holding state; a current acquisition and control unit, connected to the sample and hold unit and configured to determine whether the sample and hold unit is in the holding state and acquire the peak value of the current of the first pulsating waveform held by the sample and hold unit when the sample and hold unit is in the holding state; and a control unit, configured to perform two-way communication with the device to be charged to negotiate a charging mode between the adapter and the device to be charged, and configured to adjust the output voltage or output current of the adapter based on the present voltage or the current power of a battery of the device to be charged; wherein the adapter is configured to directly and without secondary filtering circuit apply the output current to the battery of the device to be charged. a power conversion unit, configured to convert an input alternating current, AC, to obtain an output voltage and an output current of the adapter, wherein the output current of the adapter is a current of a first pulsating waveform, and wherein the power conversion unit comprises an AC input end, a primary rectification unit, a transformer, a secondary rectification unit, and a first rectification unit, the primary rectification unit being configured to transfer a pulsating direct current without primary filtering unit to the transformer; a sample and hold unit, connected to the power conversion unit, and configured to sample the current of the first pulsating waveform when the sample and hold unit is in a sampling state and hold a peak value of the current of the first pulsating waveform when the sample and hold unit is in a holding state; a current acquisition and control unit, connected to the sample and hold unit and configured to determine whether the sample and hold unit is in the holding state and acquire the peak value of the current of the first pulsating waveform held by the sample and hold unit when the sample and hold unit is in the holding state; and a control unit, configured to perform two-way communication with the device to be charged to negotiate a charging mode between the adapter and the device to be charged, and configured to adjust the output voltage or output current of the adapter based on the present voltage or the current power of a battery of the device to be charged; wherein the adapter is configured to directly and without secondary filtering circuit apply the output current to the battery of the device to be charged.