I've been using that charger now exclusively on my WIN2 since I got it a couple of weeks ago with no issues (I've charged with it on and with it off) -- I'm not convinced it's overvolting, everyone in Discord with new model devices is saying their fans spin up to high speed when they have it plugged in and turned on regardless of which charger they use.

I checked to be 100% sure, and my unit also switches fans to high speed using the GPD provided charger if I charge when it's powered on. I don't think it's anything to worry about, but if you're really really concerned, this isn't too expensive and can answer the question for you:

https://www.amazon.com/Satechi-Tester-Multimeter-MacBook-Samsung/dp/B01MT8MC3N

I picked up one of these devices which is very helpful to diagnose what is actually going on.