Cut each rack of ribs into two. Carefully peel of the membrane on the bone side of the ribs.
Rub in salt, ground pepper, garlic powder, and 2 tablespoons brown sugar on both sides of the ribs. Arrange the ribs upright in the pressure cooker pot with the meat side facing out.
Combine ketchup, ¼ cup (45g) brown sugar, and Worcestershire sauce in a small bowl. Spread sauce over the ribs. Pour water into the bowl and stir to mix in remaining sauce. Then pour this mixture into the pot.
Close and lock the lid. Turn steam release handle to “Sealing” position. Press [Pressure] and set timer to 25 minutes for fork tender ribs and 30 minutes for fall off the bone tender ribs.
When cooking cycle has completed, press [Cancel] and turn the steam release handle to “Venting” position for quick release. When the float valve drops down, open the lid carefully. Transfer the ribs to a baking tray lined with aluminum foil.
Press [Saute] to boil sauce until it is syrupy, about 15 to 20 minutes. Press [Cancel]. Ladle sauce over the ribs.
Broil ribs for 5 minutes. Remove and serve immediately.