In a small microwave-safe bowl, stir together the marmalade, soy sauce, plum sauce, vinegar and garlic powder. Cover with microwave-safe plastic wrap and vent slightly. Microwave on full power for 3 minutes. Set aside.
Fit ribs into a 10 by 10-inch microwave-safe dish. Cover with plastic wrap and vent at one corner. Microwave on 50% power 25 minutes. Carefully drain liquid from dish.
Brush ribs with 1/2 cup of the sauce. Cover and microwave on full power for 5 minutes. Let stand, covered, for 10 minutes.
Serve with the remaining sauce on the side.