the easiest way to check is to buy a "Stromverbrauchszähler" don´t know the word in english
You have to plug it in the power socket and plug the AC-Adaptor from the Asus into it.
It tells you exactly the used Ampere or Watt Numbers.
Very interesting as well for looking at the Standby Usage of any other electrical device.
They are very cheap now. So go and buy one, and let us know.