The HDMI bus is not like the USB bus designed to supply external devices with power.
The 5V (max. 55mA) serve only as a voltage signal to eg a TV from the "Stand By" mode to wake ...
A single IC, as it is frequently used in HDMI switches requires an approximately 120mA. Add to that the power consumption of LEDs etc.
Ie: This unit extracts without power supply of at least 3 connected active standard HDMI devices almost the entire current, which can lead to malfunctions (in the worst case even damage the HDMI ports of the connected equipment). My Sony TV and the Amazon Fire TV delivered eg together not enough power to activate the switch. Only after switching on the Satellitenrecievers (3.Apparatus) began the switch to work ...
The whole can only function without power supply when the connected HDMI devices overachievers the HDMI standard (that are able to deliver much more than 55mA current ...)
The manual has übrigends from a maximum power consumption of 5W. This corresponds to a maximum power consumption of 1A = 1000mA.
Because of the lack of power supply only 3 stars.