I just bought a new XPS 17 9700 and I'm having the same problem that I have with my old XPS 13 9360: 

The white charge light on the power cable where it plugs into the USB-C (the power socket, in the case of the 13) keeps going out, unless I play with the connection between the cable (not the AC cord) and the adapter.

I have to keep changing the angle between the cable and the adapter, propping the cable against something, until the light comes on and stays on.  On my old XPS 13, I finally duct-taped the cable against the adapter, which seemed to help.

Now, once the adapter warms up (and "warm" is an understatement -- these babies run hot), the problem sometimes goes away.  Sometimes.

Is this just normal behavior -- or do I have a defective brick?  It's irritating when I suddenly run out of power when I've been plugged in the whole time.  But I don't want to get into an endless-replacement thing if this is just a known bug.