I had a friend bring over a Dell laptop with a USB C port that I naively assumed had TB3 support (it was listed as being "optional" on Dell's website). Turns out that the only way to actually know was to either watch it not work with a Dock, or to go into the BIOS and witness some missing settings that indicated TB3 support was not present.
For better or for worse, though, that's a manufacturer problem - they could have easily just not allowed _any_ USB C charging and stuck with an AC adapter, or spent the extra coin to make all of the ports work with a TB controller, etc. Companies have been making user-hostile decisions in the name of cost cuttings (1366x768 screens in 2018) forever, it seems like USB C is just another avenue for that.