Combine potato starch and water in a large bowl, stirring to combine. Let sit for 1 hour or until starch sinks to bottom of the bowl and solidifies.
Season pork with salt, pepper, and minced garlic. Let sit for 20 minutes.
Meanwhile, prepare sauce. Heat 1 tablespoon oil over medium heat in a wok or medium saucepan. Add onions, carrots, and bell peppers and cook until softened, about 6-7 minutes. Add pineapple with its juices, water, sugar, vinegar, and soy sauce. Stir to combine and let simmer for 3-4 minutes. Combine ¼ cup cornstarch with ¼ cup water and add to sauce. Continue to simmer until slightly thick, about 2-3 minutes. Keep warm.
Preheat frying oil to 350 degrees F.
Drain water from potato starch and water mixture. Add egg white and mix until well combined. Add pork to the starch and mix to coat. Carefully add a small batch of the pork to the frying oil and fry until crispy, about 3-4 minutes. Remove and drain on a paper-towel-lined tray. Repeat with remaining pork.
Fry the pork once more.
Combine soy sauce and rice vinegar for dipping sauce. Serve pork with sweet and sour sauce on top or on the side. Dip pork in sweet and sour sauce followed by the soy sauce vinegar mixture.