After installing four AV-2000 TP-LINK Powerline adapters to connect three TVs to my cable router, I have a few comments to make that may or may not help you install yours.
1. If for some reason, you can't plug your adapter directly into a wall socket, go ahead and use a short extension cord or a small outlet strip. The company says not to do this. But I could not reach the wall outlet behind my upstairs TV, so I had to rig a tool to plug an extension cord (maybe five or six feet long) into the outlet and then plug the adapter into the cord. My reasoning is that the cord wiring is about the same size (number 16 wire compared to house wire of 14 most likely), so the adapter wouldn't really know the difference.
My kitchen TV hangs on the wall, with a two-socket outlet in a small, shallow box indented into the wall behind it. So let's count the sockets we need: cable box, TV, adapter. That's three. Well, what about the pass-through socket on the front of the adapter? Well, the adapter itself is so big that it blocks the other outlet. Not enough room in the little box to plug the adapter into the bottom outlet and besides, the cable box power supply is three inches long. Solution, a small outlet strip.
CAUTION: TP-LINK says not to do this. Why? Because if you buy a fancy outlet strip, it is likely to have power surge protection or other voltage filtration, and you might be filtering the data right out of your connection. I took my outlet strip apart first to be sure there were no add-ons. (Please don't take yours apart while it is plugged in or if you don't really know what you are doing.) It seems unlikely that the little three or four socket strips such as the ones a the dollar store will have any filtration.
2. Pairing. For both initial set up (connecting your router to the base adapter and the base to the remote adapter) I finally discovered that things work much better if you plug your remote device (TV or PC or printer or whatever) into the adapter and turn the device on.
In other words, my instructions for adding an adapter to your existing Powerline network are as follows:
Step 1: Plug your new adapter into the wall near the device you want to connect to your network.
Step 2. Using the supplied Ethernet cable, plug your device into the adapter.
Step 3. Turn your device on.
Step 4. Press the Pair button on your base Powerline adapter.
Step 5. Press the Pair button on the new adapter.
These steps saved me many failed attempts to connect.