This adapter is used to feed 5V into the HDMI line. Especially with longer HDMI distances (from 5m) it can happen that the 5V operating voltage of the HDMI source is not sufficient to transmit the signal to the receiver. As a result, for example, no clean picture or even no picture will reach the receiver. The additional USB power source, for example from a PC or an optional USB power supply, provides a better power supply. USB cable length: 0.5m