I plugged in a 110v device into a 220v plug, is it still useable?
Can you do it? Yes.Will the device be usable? Probably not.You might get a beautiful puff of smoke. Or a lovely fire.The other way round, 220V device into a 110V, will more likely just not function at all, but the electronics will not be damaged.The different plug types usually prevent you from even being able to plug the wrong plug into the wrong socket.Check on the back of the device - it might have 220/110V written , in which case it can happily be plugged into either source and function correctly. Most devices that are powered by a switch-mode power supply (SMPS) are flexible for both types (usually these are desktop computers, laptops, chargers, printers, screens, etc).Regardless, always check on the back label before sticking anything where it might not belong.