Combine all marinade ingredients. Place pork neck slices in a bowl and cover with marinade. Cover with aluminum foil and refrigerate for 2 to 3 hours.
Transfer meat and marinade to a saucepan, add water to cover, and simmer uncovered over low heat for 1 to 1.5 hours until most of the liquid has evaporated and pork reaches 63°C (145°F) internally.
Let the pork cool for 10 minutes, then cut into strips.
Heat peanut oil in a wok over high heat. Add pork strips and fry for 2 to 3 minutes until lightly browned.
Sprinkle palm sugar over the pork and cook for 2 minutes, stirring occasionally, until the sugar caramelizes.
Add onion and garlic and stir-fry for 1 minute until fragrant.
Pour vinegar into the wok to deglaze, scraping up any browned bits. Add ketchup, tomato paste, chilli sauce, and water. Stir well and simmer over medium heat for 3 to 5 minutes, until the sauce reduces slightly.