Mix together the drained pineapple juice, brown sugar, soy sauce and garlic powder together in a large plastic zipper bag then knead the bag a few times with your hands to mix the marinade and dissolve the sugar. Place the pork chops into the marinade, squeeze out any air in the bag, seal it then refrigerate overnight. Reserve the pineapple rings.
Preheat a barbecue for medium heat then lightly oil the grate.
Remove the chops from the marinade, shaking off excess then grill until browned, the meat is no longer pink inside and the meat shows good grill marks, 5 to 8 minutes per side. Brush several times with marinade and let the marinade cook onto the surface of the meat. Discard excess marinade. While the meat is cooking, place 4 pineapple rings onto the barbecue then allow to cook until hot and the slices show grill marks; serve the chops topped with the pineapple rings.