Router closet is pretty tight. No available wall plugs.  I have wifi and wired ethernet in most of my house.  Could I plug a powerline adapter (base unit) into one of those ethernet ports in another room?  Every video and instruction manual say to plug into the router, but I cannot figure out a technical reason why.

Setup would be: internet to modem to router to ethernet port in living room to powerline adapter (base unit) to 2nd powerline adapter (end point) where I don't have good wifi or wired internet coverage. At the end point will be my wired OTA DVR. Right now, without a powerline I am getting 5 Mbps (wifi) which is not fast enough for streaming.  Goal is 20 Mbps. Internet from ISP is a little more than 100 Mbps.