Power is very subjective. The FiveseveN offers impressive wounding mechanics for the recoil and a standard 20-round magazine. The Glock 20 offers incredible energy for a semi-auto with unrivaled capacity for a 10mm. The Glock 20/21 with the .50 GI conversion kit offers controlable .50-cal firepower, and the Desert Eagle offers more power in the .50-cal range (with more ammo than a .500 S&W). If you're looking for number of holes from a magazine, the Taurus Raging Judge Magnum with the 7-round cyllinder shooting 000-buck out of 3" shells can produce 35 holes.
You also gotta factor in things like a 6.8 AR pistol or a Draco AK pistol, which are legally considered handguns. 30 rounds of 7.62x39 beat out 15 rounds of 10mm any day, even out of a 7" barrel. While we're on that subject, I guess I can bring up the 100-round beta-cmag for the Glock 17, which offers a lot more firepower than a 10mm Glock with 15 rounds. Which reminds me of the Calico pistol (ugly and impractical, but still a 50-round .380 or 9mm pistol).
What are you looking for in terms of power? How many BGs (or bears) you can take down? How much energy you can impart? Total wound channel size produced by a magazine?
It is also worth noting that if the 10mm doesn't penetrate deeply enough (thinking of things like really big bears), then it doesn't matter if you have 50 rounds; 1 round of something more powerful will likely serve you better.