Remove membrane from ribs. In a small bowl, combine garlic powder, onion powder, chili powder, and cayenne pepper. Thoroughly season ribs all over.
Preheat oven to 300 F. Transfer ribs to a sheet of aluminum foil. Wrap tightly, using another sheet on top if needed. Bake until completely tender, about three and a half hours.
Meanwhile, make the glaze. In a small saucepan, combine sugar, ketchup, vinegar, soy sauce, and chili flakes. Bring to a simmer and cook until sugar is dissolved. Set aside.
Light a gas or charcoal grill to medium high heat. Place ribs on the grill and cook until slightly charred, brushing with glaze until well coated. Flip and repeat on the opposite side. Remove from grill and let cool slightly, then slice between bones.