Be sure both devices are connecting to the same radio...ie 2.4 and 5. Do you use different SSID.
Look at the status of the wifi it should show you a connection "speed" . This number actually represent the data encoding. This is as important as the db number. A very weak signal with little interference will work as good as a stronger signal with more interference.
It really doesn't matter the wifi will attempt to connect at the fastest data encoding it can negotiate and there is not much you can do to change it. Since the desktop adapter has a USB cable try to place the unit in a slightly different locations and see if it changes anything. You want it away from the big metal box of your computer to avoid blocking the...