Heat the oil in the pressure cooker. Saute the onion until tender. Set aside. Brown the chops on both sides (use more oil if needed).
Arrange the chops in a single layer in the pressure cooker. Add the beef stock, wine, thyme, sugar, salt and onion. Close the cover securely. Place the pressure regulator on the vent. Cook for 9 minutes at 15 pounds - start timing when the pressure regulator begins to rock. Immerse the pressure cooker in or under cold running water to stop the cooking immediately. Remove the cover. Remove the chops. Serve on a bed of cooked white rice.