It's very mysterious that it's so particular about the charger. The XPS 13's battery is only 7.4V, so that's not the reason (a simple charging circuit needs a higher input voltage than the top voltage of the battery it's charging).

It's hard to say that the poor implementation of USB-PD ruins the XPS 13, because it's overall a great laptop. But it is very annoying to travel with this computer, realize that you brought only an 18w or 30w charger, and contemplate how nearly every other device you have works fine with it. And every year since 2016 I decline to upgrade my XPS 13 because they haven't fixed this (moreover they probably don't even consider it a problem).