Heat oven to 350'F. In large bowl, combine potatoes, melted butter, salt, pepper, and garlic powder. In another bowl, combine cheese, SPAM, soup, sour cream, milk, onion, and green chilies. Add SPAM mixture to potato mixture; mix well. Pour into 2-quart baking dish. Sprinkle with potato chips. Bake 45-60 minutes or until thoroughly heated.