A dongle for coupling a signal source device and a signal sink device is disclosed. The dongle includes an interface receptacle, a display port interface plug, a repeater, a low-dropout regulator and an impedance unit. The interface receptacle is a DVI receptacle or a HDMI receptacle. The repeater is electrically connected between the interface receptacle and the display port interface plug to enhance signals. The low-dropout regulator includes a power input end and a power output end. The power input end is electrically connected to the interface receptacle, and the power output end is electrically connected to the display port interface plug. The impedance unit is electrically connected between the power output end of the low-dropout regulator and the interface receptacle. The signal source device may output the display port signal needed by the signal sink device according to the function of the dongle.