That's unfortunate. Which model do you have? We use models from the past 5 or so years, all with Nvidia cards, the only recent issue we've had was with a new model that arrived yesterday and Ubuntu 18.04 didn't have a wireless driver, but quick connection over ethernet and an update fixed that.
You also have to switch RAID to AHCI out of the box (if it came with Windows) but it's otherwise been smooth sailing from there.
As for graphics, Prime/Primus/Optimus (which ever it is, I'm never sure) is an issue with all machines and not a DELL issue, Linux support, in my experience, for switchable graphics is just terrible.
The machine I'm on now (XPS 15 9560) has nvidia always on, I used it plugged in 99% of the time anyway, I'm running Ubuntu 18.04 for work.