Add the chopped onion, celery, ground black pepper, and garlic powder. Cover and boil in medium heat for 30 minutes.
Add the pork baby back ribs. Cover and simmer for 60 to 90 minutes. (note: you can cook faster by boiling for 45 minutes, but simmering will make the meat more tender and will bring out the flavor). Add more water as needed.
Put the potato and cabbage in the soup pot. Stir. Cover and boil for 5 minutes.
Add the baby bok choy and stir-in the fish sauce. Cook for 1 minute.