In medium bowl, combine cream cheese, Monterey Jack cheese, onion, mayonnaise, garlic powder and chiles; mix well. Stir in dried beef. Spoon into 1 or 1 1/2-quart slow cooker.
Cover; heat on Low setting 1 1/2 to 2 hours.
Just before serving, sprinkle pecans over top. Dip can be kept warm in slow cooker for up to 1 hour. Serve with crackers or cocktail bread.