In a large mixing bowl, combine the frozen shredded potatoes, melted butter, sour cream, condensed cream of chicken soup, shredded cheddar cheese, chopped onion, garlic powder, and black pepper. Stir the mixture until all ingredients are thoroughly mixed.
Transfer the mixture into the crockpot. Spread it evenly across the bottom.
Cover the crockpot and set it to cook on low for 3 to 4 hours, or until the potatoes are tender and the casserole is heated through.
Once cooked, give the casserole a gentle stir and serve warm.