Spray the slow cooker with non-stick spray, set aside. In a extra large bowl, stir together the sour cream, 3 cups of the cheese, salt, pepper and onion powder. Add in the frozen hash brown and stir until there is sour cream mixture coating all the hash browns.
Add the cheesy hash brown mixture to the sprayed slow cooker.
Cover and cook on HIGH for 3 hours and 20 minutes. Add remaining cheese (1 cup) and put the lid back on until the cheese melts.