Spray your slow cooker with non-stick cooking spray to make cleanup a breeze.
Add cream cheese, sour cream, heavy cream, garlic, onion powder, salt, and pepper to the slow cooker. Stir to combine.
Mix in the cheddar cheese, mozzarella, and Parmesan cheese, stirring well.
Fold in the chopped broccoli florets until everything is evenly distributed.
Cover and cook on LOW for 2 hours, stirring every 30 minutes to ensure even melting and prevent edges from burning.
Give it a final good stir and switch to WARM setting for serving. Serve with tortilla chips, crackers, toasted baguette slices, or veggie sticks.