Combine pork cubes, soy sauce (toyo), Chinese cooking wine, and black pepper in a bowl. Mix well and let marinate at room temperature for 30 minutes or up to 4 hours in the refrigerator. If refrigerated, remove from the fridge 30 minutes before cooking to bring to room temperature.
While the meat marinates, prepare your sauce. In a medium bowl, whisk together pineapple juice (katas ng pinya), rice vinegar (suka), ketchup, brown sugar (asukal na pula), salt (asin), and cornstarch until smooth and well combined. Set this aside.
After marinating, drain the pork well and pat each piece thoroughly dry with paper towels (Patuyuin ng mabuti gamit ang paper towel). This step is crucial for achieving crispy pork.
Mix your coating ingredients in a shallow dish: all-purpose flour (harina), cornstarch (corn starch), salt (asin), and white pepper. Take each piece of marinated pork and coat it thoroughly in the flour mixture, shaking off any excess (Alisin ang sobrang harina). Place the coated pieces on a clean plate.
Heat your oil in a deep, heavy-bottomed pan or wok to 325°F (163°C). Use enough oil to submerge the pork pieces. While waiting for the oil to heat, prepare a plate lined with paper towels for draining.
Once the oil reaches temperature, begin your first fry. Work in batches, carefully adding several pieces of coated pork to the hot oil (Mag-prito ng kaunti lang kada batch). Fry for 3-4 minutes until light golden. Remove and place on the paper towel-lined plate. Continue until all pork is fried once.
Increase your oil temperature to 350°F (175°C). This second frying will create the ultimate crispy exterior. Return the pork pieces to the hot oil in batches and fry for an additional 2-3 minutes until deeply golden brown and crispy (Iprito muli hanggang maging golden brown at malutong). Remove to fresh paper towels.
In a clean wok or large pan, heat 1 tablespoon of oil over medium-high heat. Add your sliced onions (sibuyas) and bell peppers. Stir-fry for 30 seconds until just starting to soften but still crisp (Igisa hanggang malambot-lambot).
Pour in your prepared sauce mixture and bring to a boil, stirring constantly. Cook until the sauce thickens and becomes glossy, about 2-3 minutes (Lutuin hanggang lumapot ang sarsa). Add the pineapple chunks and cook for another 30 seconds.
For serving immediately, add the crispy pork to the pan and quickly toss to coat with the sauce. If you plan to serve later, keep the sauce and pork separate until ready to eat.
Serve immediately over hot steamed rice (mainit na kanin). For best results, the pork should be sauced just before eating to maintain maximum crispiness.
To store leftovers, keep the sauce and pork separate in airtight containers in the refrigerator for up to 3 days. When reheating, warm the pork in a 350°F (175°C) oven for 5-7 minutes until crispy again, and heat the sauce separately in a microwave or on the stovetop until bubbling.
Remember: The key to perfect sweet and sour pork is maintaining the crispiness of the meat while balancing it with the tangy-sweet sauce. Don't let the pork sit in the sauce too long before serving.