Computers have a network card that when the user sets it up allows connecting to your ISP account. Have you created a Windows network using the built-in network card in the PC? You don't need an adapter unless that network card is broken.
The same exact thing can be said of the Mac.
All Windows PCs that are anywhere near new enough to have ever used the internet at all, came with a network card installed. Is the one in your PC broken? If not, why not use it?
OK, well ... If you were using an adapter and it broke, the simplest thing to do is replace the adapter and forget the sharing thing. Just like tires on your car, if you blow out a tire you buy another tire. You don't try and figure out how to share a tire on hubby's truck.
But, what I'm saying is the built-in network card in your PC IS an adapter of sorts, You already have a replacement right there. That is unless the Windows PC is running Windows 3.1 or something that old maybe.
If your PC operates poorly with respect to the internet, sharing a signal with the Mac is not going to improve things. If anything it will make matters worse because of sharing a limited resource and diluting signal strength.