tried several chargers get message "this device may not be supported"

I've had this problem before, try a different outlet, and it should work better there. It's not the charger, and it worked for me the next day in the regular outlet, so just try a new one and see what happens.

If you are using an Apple Lightning cable and Apple USB adapter (neither of them are a "charger" - the charger is in the phone) then the problem is most likely dirt or pocket lint in the Lightning port on the phone. Check it with a bright light, clean it with a toothpick.