Heat an air fryer to 400°F. Meanwhile, drain 1 (16-ounce) jar pickle chips or ovals. Place the pickles on paper towels in a single layer, then pat the tops dry with more paper towels.
Place 1 large egg white in a medium bowl and whisk until soft white peaks form, about 5 minutes. Add the pickles to the egg white and stir gently to coat.
Place 1/2 cup yellow cornmeal, 1/3 cup all-purpose flour, and 1 tablespoon Cajun seasoning in a large zip-top bag. Seal the bag and gently shake to combine.Transfer the pickles to the bag. Seal again and shake the bag to coat the pickles evenly in the cornmeal mixture, pressing gently to help the coating adhere to the pickles. Separate any pickles that may have stuck together and toss again with the coating.
Coat the air fryer basket with cooking spray. Working in 2 batches, place the pickles in a single layer in the air fryer basket and spray the tops with more cooking spray. Air-fry until lightly golden and crispy, 10 to 15 minutes. Before adding the next batch, shake the bag to redistribute the coating over the remaining pickles.
Meanwhile, make the dipping sauce: Place 1/4 cup mayonnaise, 3 tablespoons ketchup, 1/2 teaspoon black pepper, and 1/4 teaspoon garlic powder in a small bowl, and stir to combine.
Serve the pickles warm or at room temperature with the dipping sauce.