Spray slow cooker with nonstick spray.

Mix cream cheese, sour cream, heavy cream, garlic, onion powder, salt, and pepper in cooker.

Stir in cheddar, mozzarella, and Parmesan thoroughly.

Fold in broccoli evenly.

Cover; cook on low 2 hours, stirring every 30 minutes for even melting and to prevent burnt edges.

Stir thoroughly; switch to warm. Serve with tortilla chips, crackers, toasted baguette, or vegetable sticks.