In a large bowl, combine the cream of chicken soup, sour cream, cream cheese, and butter. Add in 1/4 cup of the cheddar cheese, all but 1 tablespoon of the green onions, the milk, garlic powder, salt and pepper and stir until everything is mixed together. Gently stir in the cooked potatoes, trying not to mash them too much. Pour the creamy potatoes into a large rectangular baking dish and transfer to the oven.
10 ounces cream of chicken soup, 1/2 cup sour cream, 4 ounces cream cheese, 2 Tablespoons salted butter, 3/4 cup medium cheddar cheese, 1/3 cup chopped green onions, 1/4 cup milk, 1/4 teaspoon salt, 1/8 teaspoon garlic powder, 1/4 teaspoon black pepper