I bought an xps 15 9560 ( used one ) , and i am surprised that checking system property its showing ASUS instead of DELL . But when check dxdiag command output it show the right manufacturer DELL and the right model XPS 9560 , also when i connect to dell support website and try "Detect product" option it shows the right model with the right service Tag and Express service code .
Also after the first update i did for windows , now windows showing that it will expire end of Month.
Contact the seller - someone used an ASUS version of Windows on the system. At a minimum you'll need to reinstall WIndows on the system - and while the mainboard SHOULD have an embedded product key, if it doesn't, you'll need to go back to the seller to obtain a license key.