XPS 12 comes with only with Intel HD 4000 Graphics card. If you wish to connect 2 monitors, then you would need to use a splitter (see image).
XPS 12 comes with 12.5 inch LED Backlit Touch Display with Truelife and FHD resolution (1920 x 1080).
as i undrestand dell U2713HM supports mDP 1.2 which supports monitor daisy chaining. (so spliter is not needed ). only questions is does xps 12 support two monitors with 2560x1440 resolution.
XPS 12 does not support dual display. By using a splitter, you can connect 2 monitors but you may not get 2560x1440 resolution.
Unfortunately after many hours with Dell on the phone I reached the right person and the answer is NO.
1. The card output is not capable to run external monitors bigger than HDMI which is 1920x1080.
2. It runs OK with HDMI cable or through the docking station and DVI
3. You cannot run different displays but one for both (extended) not very convenient - one is 13 inch the other is 24 in my case.
Hope this helps.