Thunderbolt doesn't work on two consecutive XPS 13 9380

I've ordered an XPS 13 9380: when i wanted to connect it to my TV screen with an USB-C to HDMI adapter (adapter that worked flawlessly with my previous XPS 13 9360), an error message popped up (saying that usb peripheral wasn't recognised). I've called dell's hotline, whose technician ran several tests before announcing that this PC needed a mainboard replacement...

I've thus replaced this computer with a new one. The same problem happened. 

So here's my question: Does the XPS 13 9380 REALLY supports thunderbolt 3?