One shouldn't need to be all that careful about what to plug in. The only thing that should happen when a charger and a device doesn't support the same fast charging standard, is that the charger should stick to the standard USB specification and stay at 5Volt.
That's why I can safely plug my (up to) 130W Dell USB-C charger (it's a powered docking station for a laptop, to be precise) into my Cosmo, and it will even work, though at 5V ~10W, with no fast charging. Only when that charger gets the secret handshake from a Dell laptop, will it kick the voltage up to 19.5V and allow 6.7A (which is beyond the USB PD standard, but that's how Dell did it).
FWIW, I have charged both my Gemini and Cosmo with various Samsung chargers many times. While the device, of course, wouldn't fast charge, it charged just fine. There is, of course, always the possibility that some chargers, especially off-brand models, might not follow the standards properly, so applying a bit of common sense is typically beneficial.