For those who speak japanese, it depends whether you divide the phrase into "[kono Uchiha Madara] [no chikara] ga" or "[kono Uchiha Madara no chikara] ga". Japanese is a tricky language, context makes things complicated.
Its already divided
Kono Uchiha madara no
The「が」(ga) particle identifies a specific property of something.
That would be of Tobi, property that he possess that of uchiha madara power
So, Tobi possess the power of Uchiha madara.. so "My power, Uchiha madara power" is the right translation, not that he is Madara himself, merely that he have the same power as madara
"Chile is a thin and tall country"