@pabzter
Thank you for your answer and your offer to test it, but GL.inet already sent me an mail. It are max. 2 Watt. They had the wrong value in the specs. Now there have corrected the specs at their homepage.
I want to operate the router with a solar panel. My solar “construction” reliably provides about 0,5A at 5 V. So 2 Watt should be ok, 3 Watt could make problems. Thats why the power consumtion is important for me. I also have a USB power meter, but i dont have a GL-MT300A to test it. Therefore I wanted to know the power consumtion before buying it.