To make the marinade, mix the shaoxing, kecap manis and oyster sauce. Add the beef and toss until well coated, then leave for 20 minutes.
Heat a wok until just smoking. Add half the oil and, when hot, stir-fry the beef in batches until well browned, then remove. Add the remaining oil to the wok and stir-fry the onion, capsicum, chilli, garlic and pepper until fragrant. Return the beef to the wok with the stock, soy and oyster sauces and stir-fry until the sauce reduces slightly.