You just described a WiFi Client device. These take in WiFi and have an Ethernet port for you to plug into your powerline device.
There are hundreds of these things. I'll just supply one cheap I owned back them. It does a lot of things besides the client trick.
https://www.amazon.com/TP-Link-Wireless-Travel-Extender-TL-WR702N/dp/B007PTCFFW
As you know powerline, I don't need to show examples.
I am looking for a neat solution for my (UK) neighbours with a large house with thick radio-absorbing walls. Powerline is the obvious approach, but ...
... the house has been created from two properties, and they have not merged the electricity supplies: they have two meters and consumer units covering different parts of the house. The two meters are at opposite ends of the house.
The challenge is to get an internet signal from the router at ground level on Meter A to feed as a Powerline signal into the mains supply on Meter B.
Cosmetic appearance is important. Running a Cat-5 cable between Powerline modules in the two zones of the house does not look viable.
So I am looking for a unit that will connect to the router via wifi, and then broadcast over Powerline. While there are plenty of powerline+wifi units available, the normal configuration is powerline upstream and wifi downstream. I am looking to work the other way around. Suggestions?

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