Preheat the oven to 350 degrees. In a medium bowl, mix together the sour cream, cream cheese, and mashed potatoes until smooth. Add ¾ cup of the cheddar cheese, most of the bacon bits, and most of the green onions, onion salt, and garlic powder. Mix together. Pour into a small casserole dish, coated with non-stick cooking spray, and top with the remaining cheese. Bake for 30 minutes or until the cheese is melted and bubbly around the edges. Top with the remaining bacon and green onions. Serve with your favorite dippers.