The router’s supplied power adapter is rated 15 watts, although it may normally use somewhat less.

If you’re not plugging something in, it will always use substantially less. I’ll run the numbers in a couple of hours, but you’re probably looking at more like 3W.

Basically if you can run an external hard drive on your USB port, you can run one of these routers (as long as you’re not chaining things on past the router). All of this fear mongering about needing a 5V/4A source is getting out of hand.