I agree that ASUS should have written this somewhere in the documentation. The other thing is if you look at the back of the adapter where the specifications are, you might notice the bunch of standards that are met. I am pretty sure if we can find w...
I have similar symptoms. I did notice that this happens when your adapter is plugged in the socket without any load. So I think this is some power saving feature of the charger. It turns itself off when idle. I think this is also good for the charger...