Well, I'm pretty sure that the power adapter NOT PLUGGED INTO MY LAPTOP AT ALL is less than 75W.

I did not know going in that there was a 75W limit. It did occur to me that I was pulling too much power when I was on the plane and it wasn't working, but I also know that my laptop's power adapter is about as small as they come.

And just checked the label - it's a 65 watt adapter.

Either way, plugging in either the adapter alone or the adapter plugged into a laptop that had no battery and was OFF still knocked out the green light.