@Roger_jay I had the same exact problem.  Brand new TP-Link on my desktop. At command prompt typed "netsh wlan show interfaces" as the signal was 44% at best.  This is close to router.  Notebook in any location was 99%.  I switched the TP-Link to my notebook and it dropped down to the same 44%.  I used the latest drivers, which is to say two years old, from this site.  I am not a happy camper.

Roger_jay wrote

Region : UnitedKingdom

Model : TL-WDN4800

Hardware Version : V1

Firmware Version :

ISP : PlusNet

Hi


I bought an AC600 Archer T2U to use with my desktop.


Speed of the Wireless connection to the router is at 72Mps
Signal strength from the TP utility is at 70% "excellent"


But internet speed is below 2Mb, a tenth of that of my laptop (20-25Mb) in the same room, next to the desktop.


When I used the Adapter with my laptop (instead of that of my laptop) the speed fall to that of the desktop.


Is this adapter faulty?


Thx