The present disclosure discloses a charging device, a charging method, a power adapter and a terminal. The charging device includes a charging receiving terminal, a voltage adjusting circuit and a central control module. The charging receiving terminal is configured to receive an alternating current. The voltage adjusting circuit includes a first rectifier, a switch unit, a transformer and a second rectifier. The first rectifier is configured to rectify the alternating current and output a first voltage. The switch unit is configured to modulate the first voltage to output a modulated first voltage. The transformer is configured to output a second voltage according to the modulated first voltage. The second rectifier is configured to rectify the second voltage to output a third voltage. The voltage adjusting circuit applies the third voltage to a battery directly.