Spray your slow cooker lightly with non-stick cooking spray.
Add the cubed cream cheese, shredded cheddar, Monterey Jack, mayonnaise, and sour cream to the slow cooker.
Stir in the drained pimentos, green chiles, garlic powder, onion powder, and cayenne pepper (if using).
Cover and cook on LOW for 1.5-2 hours, stirring every 30 minutes to ensure even melting and prevent sticking.
Once the cheese is fully melted and the mixture is smooth and creamy, stir well to combine everything.
Switch to the "warm" setting and serve directly from the slow cooker with crackers, bread rounds, or fresh veggies.
