The present disclosure discloses a charging device, a charging method, a power adapter and a terminal. The device includes: a charging receiving terminal configured to receive a first alternating current; a voltage adjusting circuit, including a first rectifier configured to rectify the first alternating current and output a first voltage with a first pulsating waveform, a switch unit configured to modulate the first voltage according to a control signal to obtain a modulated first voltage, a transformer configured to output a plurality of voltages with pulsating waveforms according to the modulated first voltage, and a synthesizing unit configured to synthesize the plurality of voltages to output a second alternating current; and a central control module configured to output the control signal to the switch unit so as to adjust voltage and/or current of the second alternating current in response to a charging requirement of the battery.