Has been almost a year that I bought my dell XPS developers edition with the DA200 adapter, which only works with low resolutions due to a published bug. http://en.community.dell.com/support-forums/software-os/f/3525/t/19999974 . Other USB-C to HDMI adapters / docks also fail with the same.
During all this time there was no solution without compiling and patching the kernel, as described here : https://patchwork.kernel.org/patch/9646451/ .
I was using Ubuntu 16.04.3 LTS with the Kernel 4.10 before the upgrade, with the latest Intel drivers and Gnome Shell enviroment.
On the 3rd of September of 2017, the Linux Kernel 4.13 was released, and included the patch about this particular driver. You can see more information about this here : https://lkml.org/lkml/2017/9/3/155
What we are going to do now, is simple install this version of the kernel in order to fix the issue. By the way, in this moment I am writing with my external monitor connected through my USB-C/HDMI converter.