After moving house I had to use a wifi connection to my wife's Dell Optiplex 780 that was positioned around a corner in the conservatory. Bought a PCI wifi card with aerials attached, installed it, then found the 780 can't cope with the display port as well as a PCI card!! Darn, didn't see that coming.
Next was a USB 2.4Gb doofer. It was coping with browsing but I was finding macrium backups were VERY slow and usually failed.
Now I have a D-Link AV2 1000. Wow, instant success with 104/25 off my 100/20 connection. Even came with the two connecting cables.
Now wonder why I didn't get it to start with.