Abstract: A mobile high-definition link with built-in power supply includes an adaptor module, a power supply module, and a battery. The power supply module is automatically or manually switchable between the battery and an external power source. When a transfer unit is to transfer a signal from a smart mobile phone or a tablet computer to a displaying device, a detection module automatically activates the transfer unit by using electrical power supplied from the power supply module. The power supply module may select the battery or the external power source based on a result of detection so as to realize a power saving function of automatic detection and activation/deactivation of the battery power source and also provide an advantage of requiring no seeking for an external power supply.