Full form of switch mode power supply?

Answer 1

An auto-switching power supply is one which can switch between power inputs instantaneously, preventing a loss of current to the machine.

These power supplies may have redundancy built into them (in effect, they may be one or more traditional power supplies built to work together), or they may not. the key is that they have multiple power inputs (usually in the form of two or more power cords), and can chose which ones to draw power from.