A charger and a charging system are provided. The charger includes: a rectifier, a transformer, a first diode, a capacitor, a voltage sampling feedback unit, a pulse width modulation (PWM) controller, a battery voltage feedback unit and a semiconductor switching component, where the battery voltage feedback unit is added in the charger to detect battery voltage of a terminal, and the detected battery voltage of the terminal is fed back to a voltage sampling feedback unit inside the charger, so that the voltage sampling feedback unit can adjust an output voltage of the charger in real time according to an actual battery voltage of the terminal, and therefore, the output voltage of the charger gradually rises along with an increase of the battery voltage of the terminal, thereby effectively reducing energy consumption of the charger and achieving a purpose of energy saving.