XPS 13 9350 Flickering external monitor using USB-C to HDMI adapter

My XPS13 9350 was one of the first with USB-C port (Thunderbolt 3) only and no DisplayPort, supplied in early 2016. It has caused a lot of headaches. As I tried to connect my external Dell monitor using  a USB-C to HDMI adapter from Dell (part no: 47KD7) there was no external display at all. Dell Support advised me to update BIOS. But it led to a complete freeze of my laptop and Dell replaced the motherboard. (It was a real nuisance as I use my laptop for work!!)

With the new motherboard,  the laptop/USB-C adapter/external monitor worked fine for 15 months. Until one day, out of the blue, the external screen started flickering with an image that was all distorted (cut in the middle). The laptop screen was fine. After a few weeks of flickering, there is no signal at all to the external screen. Moreover, as I connect the adapter in USB-C port the resolution on my laptop screen changes.

I know there have been a lot of issues with USB-C connector on XPS 13 and 15.  I have reduced wifi-power to 50%  but it has had no positive effect (several persons have said on this forum that it helped the video output). 

I am grateful to learn if anybody with similar problems found a solution. 
Cheers