XPS 13 - 9350 HDMI second Monitor error

Hi everyone,

A few weeks ago I want to use a HDMI Monitor with my XPS but it didn't work. Half year ago it was working with this HDMI adapter. I am using Windows 10 Ver. 1803. All drivers are up-to-date. When I plug in the adapter and connect it to a Monitor, the Computer recognizes that a Monitor is plugged in but as soon as I want to extend or mirror the monitor the configuration jumps back to single monitor mode. I don't understand why I am not able to change the config to second monitor when I can see the second Monitor in display config. So I tried to figure out what the problem is.

Here some other investigations I mage:

• Tried other USB-C HDMI Adapter - unsuccesfull.
• Tried driver downgrade (BIOS, chipset, graphics, thunderbolt, displaylink) to a lower version (from half year ago and some older).
• Install new Windows 10 in older Version (1709) and only driver from 2017 - unsuccessfull.
• BIOS Intel Hardware Check - ok
• checked BIOS Settings for Thunderbolt Security - ok
• Tried to boot with UBUNTU Live USB stick to check if HDMI works here - sometimes it works - not with every adapter.

Can somebody please help? How can I investigate what the Problem is and how can I get it to work again?

best regards

Ecki