Nothing will happen most of the time. Cheapo chargers are usually flyback design which is immune to this.

Anyway if you connect anything non-compliant together anything can happen. My point was that always on 5V is no problem for compliant device on the other side.

Normal people don't connect two chargers together. :) You can create all kind of fun combos though. Like connecting your PC via USB-A port to a type-c charger, etc. It's all by design safe. USB-A will provide power no matter what, it doesn't matter what CC signals are.