Home plug question.

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Lately my android box in my living room has been loosing signal. I thought it was the box so swapped it with my other one and it happened again so I'm guessing it's interference on the 2.4ghz frequency. It never happens the other box in the kitchen or with tablets phones etc, just the box. I changed channels and tried using the 5ghz but that will only connect sometimes, others it can't even be found.

I figure a home plug will sort it but, I've no socket where the router is. I've a home made extension cable running about 15ft from the router to a socket.
So my question is(eventually)
Am I better off running an ethernet cable from the router to the socket and plugging it into the home plug there so it goes directly into the house's wiring, or put the home plug into the end of the extension cable which will be much tidier.
I've read that extension leads can affect the performance of the home plugs. I'm currently getting about 35/40mbps wirelessly, I figure if I got 15/20mbps wired into the box it would be plenty for what I need.
Any ideas?
Thanks.

ED E

Get a passthrough one, try it at the router and move it later if rates suck.