Q. How can you know whether you are getting AC or DC power supply from a device?

Answer

The best way to know if you have an AC to DC power supply or a DC to DC device is to look at the device itself. In all cases, the input and output information is printed somewhere on the surface of either the adapter connecting the device or on the device itself. So if the input of the device is AC, it means that you have an AC to DC power supply, and if the input and output both are DC then you have a DC to DC model.