Add the sliced potatoes, diced ham, and diced onion to the crockpot and stir gently to combine.
In a mixing bowl, whisk together the cream of chicken soup, milk, garlic powder, salt, and black pepper until smooth.
Pour the soup mixture over the potato and ham layers and stir lightly to coat everything evenly.
Sprinkle 1 cup of the shredded cheddar cheese over the top, then cover and cook on low for 6 hours.
In the last 30 minutes of cooking, sprinkle the remaining 1/2 cup of cheese on top, replace the lid, and let the cheese melt before serving.