A power adapter configured to directly charge a battery of a device via an alternating current, AC, voltage, comprising: a first rectification unit, configured to rectify an input alternating current and output a voltage with a first pulsating waveform; a switch unit, configured to modulate the voltage with the first pulsating waveform according to a control signal; a transformer, configured to output a voltage with a second pulsating waveform according to the modulated voltage with the first pulsating waveform and to output a voltage with a third pulsating waveform according to the modulated voltage with the first pulsating waveform; a synthesizing unit, configured to synthesize the voltage with the second pulsating waveform and the voltage with the third pulsating waveform to output a second alternating current, wherein the synthesizing unit includes two controllable switch circuits and a control module configured to control the two controllable switch circuits to switch on and off alternately to output the second alternating current, wherein for each cycle of the second alternating current, an absolute value of a peak voltage of a positive half is greater than an absolute value of a peak voltage of a negative half; a first charging interface, coupled to an output end of the synthesizing unit, and configured to apply the second alternating current to the battery in the device via a second charging interface of the device when the first charging interface is coupled to the second charging interface, in which the second charging interface is coupled to the battery; a sampling unit, configured to sample a voltage and/or current of the second alternating current to obtain a voltage sampling value and/or a current sampling value; and a control unit, coupled to the sampling unit and the switch unit respectively, and configured to output the control signal to the switch unit, and to adjust a duty ratio of the control signal according to the current sampling value and/or the voltage sampling value, such that the second alternating current meets a charging requirement of the device. a first rectification unit, configured to rectify an input alternating current and output a voltage with a first pulsating waveform; a switch unit, configured to modulate the voltage with the first pulsating waveform according to a control signal; a transformer, configured to output a voltage with a second pulsating waveform according to the modulated voltage with the first pulsating waveform and to output a voltage with a third pulsating waveform according to the modulated voltage with the first pulsating waveform; a synthesizing unit, configured to synthesize the voltage with the second pulsating waveform and the voltage with the third pulsating waveform to output a second alternating current, wherein the synthesizing unit includes two controllable switch circuits and a control module configured to control the two controllable switch circuits to switch on and off alternately to output the second alternating current, wherein for each cycle of the second alternating current, an absolute value of a peak voltage of a positive half is greater than an absolute value of a peak voltage of a negative half; a first charging interface, coupled to an output end of the synthesizing unit, and configured to apply the second alternating current to the battery in the device via a second charging interface of the device when the first charging interface is coupled to the second charging interface, in which the second charging interface is coupled to the battery; a sampling unit, configured to sample a voltage and/or current of the second alternating current to obtain a voltage sampling value and/or a current sampling value; and a control unit, coupled to the sampling unit and the switch unit respectively, and configured to output the control signal to the switch unit, and to adjust a duty ratio of the control signal according to the current sampling value and/or the voltage sampling value, such that the second alternating current meets a charging requirement of the device.