Cut onions into very thin slices; separate into rings.
In med. bowl, combine pancake mix, sparkling water, chili powder and salt; beat until smooth.
In lg. saucepan or deep fat fryer, heat oil to 375 degrees. Stir onions into batter. With 2 forks, lift onions from batter in small portions. Drop into hot oil just until surface of oil is covered with onions; fry 1 - 2 min. or until crisp and browned. Remove onions from hot oil; drain on paper towels. Repeat with remaining onions. Place fried onions on ungreased cookie sheet. Cover; refrigerate.
In small bowl, combine sour cream and taco seasoning mix; blend well. Cover; refrigerate.
Before serving, heat oven to 375 degrees. Bake 10 min. or until crisp. Stack onion rings on serving platter; serve with dipping sauce.