In reference at this topic which is closed, I confirm that I have the same problem.

I've ordered XPS 27-7760 (Europe/France in June 2017) with AMD R470X and receive with AMD R390X.

I never seen that before, but recently trying to read 4k movies and horrible stutter and unwatchable. So I investigate and find that I haven't the good card on my computer.

I've write a message to the french technical support and waiting for their answer.

I didn't know that this king of thing was possible by Dell.

Regards.