Seconding Startech - I bought a DP to DVI-D adapter for my MacBook Pro and while it worked flawlessly with my PC, macOS was only showing me 1280x800 resolution instead of the monitor’s full 2560x1600 resolution. I found that under Windows on Bootcamp it fully worked on the same hardware so it was clearly a macOS thing.

Emailed their support about it and within a day, got a guy who immediately gave me very technical and specific advice and suggestions, clearly very experienced. We weren’t able to solve it (chalked it up to a weird macOS limitation and work gave me a different adapter that worked) but he was still incredibly helpful, and I’ll have confidence in buying from them in the future that their support should be excellent.