Cut onions into very thin slices; separate into rings.
In medium bowl, combine pancake mix, sparkling water, chili powder and salt; beat until smooth.
In a large saucepan or deep fryer, heat oil to 375. Stir onions into batter. With 2 forks, lift onions from batter in small portions. Drop into hot oil just until surface of oil is cover with onions; fry 1 to 2 miniutes or until crisp and browned.
Remove onions from hot oil; drain on paper towels. Repeat with remaining onions. Refrigerate.
In a small bowl; combine sour cream and taco seasoning mix; blend well. Refrigerate until ready to use.
When ready to serve, heat oven to 375. Bake onions 10 minutes or until crisp. Stack on a platter and serve with dipping sauce.