Recently become unable to use my ethernet cable as my router is now too far away from my desktop. What is the best affordable wifi adapter that particularly offers significant range? Range is important as i am now several flights above the actual router position
Range is purely a function of radio transmission power which is regulated by the government.
Although most routers transmit at maximum legal power many USB devices do not. This is primarily because USB devices are marketed toward the portable market where battery life and size are as important as performance.
There is no simple way to find the data on transmission power. They have to report this to the FCC and you can dig them out of the reports but it is very tedious.
In general what you look for on a desktop device is something that already has a USB cable so you can place it top of the machine away from all the metal on the back. The units are generally physically larger and many have external antenna.
This does not mean they put out the full legal power it just is they are more likely too, to really be sure you have to dig.
The ones you want to avoid are those tiny devices that almost hide in the USB slot. You can get them for $5 which is why people buy them but they are the worst choice for a desktop machine.
I would consider using powerline devices instead. WiFi because of how the antenna are designed tend to put out more power in the horizontal axis than vertical so they do not work as well between floors.