A video doorbell system coupled with a ringtone generating unit is applied by a power supply adjusting method and includes a video generating module and a mode switching controller. The video generating module includes a power storing component. The mode switching controller can be switched into a first mode or a second mode in a remote controlling manner. While the mode switching controller is switched into the first mode, the ringtone generating unit is bypassed and an external power source is connected to the video generating module, so as to charge the power storing component by the external power source. While the mode switching controller is switched into the second mode, the video generating module is bypassed and the external power source is connected to the ringtone generating unit, and the video generating module can execute image capturing function via the power storing component.