I am connecting my new XPS 15 9500 via USB Type-C to the first Dell monitor (P2719HC). Then to a second Dell monitor (U2415), via DisplayPort out from the P2719HC and into the U2415. I managed to get the image, but only for 5 to 10 seconds on the three monitors. Then both monitors go black, although the extended setup seems to remain. Could anyone please help?

Note: The laptop is plugged in, as well as both monitors. It works fine with only one extended monitor at a time.

Thank you in advance for your help,