Remove 2 chiles from can; finely chop, reserving remaining chiles and sauce for another use.
Heat a large Dutch oven coated with cooking spray over medium-high heat. Add chiles, 1 3/4 cups onion, bell peppers, garlic, and chorizo; sauté 5 minutes or until tender. Add chili powder and next 7 ingredients (chili powder through corn), stirring to combine. Bring to a boil. Reduce heat, and simmer, covered, 30 minutes, stirring occasionally. Remove from heat; stir in chocolate, salt, and black pepper.
Ladle 1 cup chili into each of 12 bowls. Top each serving with 1 tablespoon sour cream and 1 tablespoon onion. Serve with tortilla chips.