Typically according to the HDMI specifications the 5V output on the HDMI connector should provide at least 50mA of current to the connected device (sink). However some source devices do not provide enough current (or the 5V output drops as the sink draws power from it). Port powered devices such as some HDMI video switches, splitters, or cable boosters/equalizers rely on the 5V from the source to provide enough current. If cable installers have a source that does not provide enough power on its HDMI output for these types of devices, this power adapter can substitute 5V from the external power supply to the downstream device.