I have the router close to one corner of the house, while the computer device in question is located in the opposite corner diagonally of the house.

The computer sometimes gets great speeds, in the high 200 Mbps, close to 300.

At other times, it only gets speeds of about 10 Mbps.

Any thoughts on why it would vary so much?

I first thought about getting a powerline from TPT and creating a mesh. But have read device here and elsewhere that if it's not on the same circuit, performance will be poor.

The alternative, a WiFi extender, is problematic as well. There's not a good spot for the extender. One wall socket power source is too far from computer and the other is too far from router. There is an ideal spot for an extender, but I would have to have a wall socket power source installed ther.ee

Any feedback / input would be most wlecome!