Place 1/2 the Cheddar cheese, chicken soup, sour cream, cream cheese, butter, salt, pepper, and garlic powder in a large bowl. Beat with an electric mixer on low speed until well blended. Stir in potatoes with a large wooden spoon until evenly coated. Transfer to a baking pan. Cover with aluminum foil.
Bake on the upper rack of the preheated oven until bubbly, about 1 hour and 30 minutes. Scatter the remaining Cheddar cheese and bacon on top; continue baking until cheese is melted, about 5 minutes. Sprinkle green onions on top.