Squadron Supreme was invented by Marvel during the 70s as a take on the Justice League. They came from an alternate Earth, and clashed with the Avengers. Mark Gruenwald wrote a 12-issue mini-series called "Squadron Supreme", which is the first in-depth discussion of the ethics of power within the superhero genre, about 5 years before Watchmen did it so convincingly, and about 20 years before the Authority and the Ultimates.
While those that came after are better, the original is still quite good, indeed.
As for "Ultimate Power", I'm assuming that the Supreme Power universe is to Ultimate Earth what the original Squadron Supreme universe is to the original Marvel Universe, and the two "crossover", but don't integrate. They just clash and that'll be that.
I quite like the idea of the original "The Avengers vs Squadron Supreme" story being ultimised by blending the Ultimate universe and the Supreme Power universe, both revised and independent versions of the original Marvel universe. It's like turning Galactus into a trilogy. Making it bigger and paying off more.
That said, as nice as the idea is, I don't think the story will be any good.
I'm not really enjoying Squadron Supreme anymore.