I give, what is it ?

I will take a stab at it. It looks like a common 3-5 kva 120/240v transformer rigged to to give an out put of either 120v on low or 240v on high. Either way the`watts available will be the same depending on its kva rating. Example if a 3 kva with an input of 120v the input amps will be 25 with an output voltage of 240v the output amps will be 12.5. Not sure of what benefit that would be. That being said I could see it of more benefit if it was a 12/240v 3kva used in a boost mode to increase a low voltage situation. Without a view of the label we are only guessing. My guess is that someone made this item up to fix a specific problem that they had. JMHO.