Heat oven to 425°F. In medium bowl, mix brown sugar, butter, vinegar, salt, garlic powder and pepper. Reserve 2 tablespoons of the butter mixture. Add apples, sweet potatoes and onion to remaining butter mixture; toss to coat. Arrange apple mixture in roasting pan or 13x9-inch (3-quart) glass baking dish. Cover tightly with foil and bake 20 minutes.