Of course it does. Instead of processor running at lower clock speeds, setting your power options to High Performance will force it at the highest. This means more heat and of course more battery consumption. That is why laptops have a separate profile for Plugged in AC and when on battery power. This way, you can choose to run at High Performance when on AC and Balanced or Power saver when you are on battery.
My advise would be to try gaming at the Balanced power profile and compare it with the High Performance to see if there is any noticeable difference when you are on AC.
I can only assume that the 18 hours on the Dell XPS 13 is probably on the 1080p InfinityEdge display screen and not the 4k one.. Probably power saver profile too. if can turbo boost and still 18hr its really godly haha
The link below can tell you more about how Windows Power Options. It is a good read.
http://www.addictivetips.com/window...r-balanced-high-performance-modes-in-windows/