Place the boneless chicken strips into a bowl with the soy sauce, Shaoxing wine, minced garlic and cornstarch. Mix and allow to marinate for at least 30 minutes.
In a saucepan, place the ketchup, rice wine vinegar, sugar, pineapple juice and soy sauce and bring to a boil. Reduce to simmer. Prepare a cornstarch slurry by mixing the cornstarch and water. Add the to sweet and sour sauce and allow to simmer for another minute. Remove from heat, cover and set aside.
To make the batter, mix together the flour, egg, cornstarch, salt, baking powder in a bowl. In small batches, take the marinated chicken pieces and toss in the batter. In a wok or frying pan, heat 1 cup of oil until hot. Fry the batter chicken pieces in the wok for for about 3-5 minutes until it's cooked and golden brown. Remove and allow to drain on a paper towel on a plate. Repeat until all the chicken is cooked.
To prepare the vegetables, heat 1 tablespoon fresh oil in a wok until hot and fry the onions and bell peppers and pineapple chunks for about 1 minute. Return the crispy chicken pieces back to the wok and pour over the sweet and sour sauce. Toss to coat, serve with steamed white rice.