Lightly grease a 5- to 6-quart slow cooker.
Add the frozen O’Brien potatoes, undiluted cream of potato soup, sour cream, garlic powder, black pepper, and salt. Stir gently until the potatoes are coated.
Cover and cook on HIGH for 2 to 3 hours or LOW for 4 to 5 hours, until the potatoes are hot and tender. Stir once if needed for even cooking.
Stir 3/4 cup of shredded cheddar into the potatoes. Sprinkle the remaining 3/4 cup evenly over the top.
Cover again and cook on HIGH for about 30 minutes, until the cheese melts and the edges bubble.
Switch the slow cooker to WARM and serve.