Yes, you did read that correctly. I’ve just put a device in my house which turns a mains power socket into a computer network socket.
The devices come in pairs: you plug one into your router and into a mains socket nearby, and you plug the other into a mains socket anywhere in the house where you want to access the internet.
Then it’s just a matter of plugging your computer into the device using a normal network cable, and away you go.
It’s great if you’ve got a house like mine over three stories, or with thick stone walls, or with corners that are hard-to-get-to for a wireless signal. It’s also much better (ie much faster) than wireless if you want to stream music or video over the internet.
Depending on the brand, they cost between about £50 and £70 a pair and the devices are interchangeable: getting two pairs gives you three output points. Search google for ‘ethernet over power‘, or drop me a line and we’ll get them for you.