Heat about 3 inches of vegetable oil in a deep, heavy-bottomed pot over medium heat until it reaches 350°F. Use a thermometer to monitor the temperature for the best results.
In a medium bowl, combine 1 1/2 cups pancake mix, 1 large egg, 1 cup milk, and 2 teaspoons vegetable oil. Stir just until the batter is smooth and combined. Do not overmix.
Using a fork, dip each of the 20 Oreo cookies into the pancake batter, turning to coat completely. Allow any excess batter to drip back into the bowl.
Carefully place the battered Oreos into the hot oil, working in batches to avoid overcrowding the pot. Fry for 3 to 4 minutes, turning occasionally, until golden brown on all sides.
Using a slotted spoon, carefully transfer the fried Oreos to a paper towel-lined plate to drain.
Arrange the warm fried Oreos on a serving plate and dust evenly with 1/4 cup powdered sugar. Serve warm.