Heat oil in a large skillet over high heat. Place the pork in the oil and sprinkle with salt. Fry for 5 to 10 minutes, or until brown on all sides. Remove the pork from the oil, cover with foil to keep warm, and set aside.
In the same skillet over medium heat melt the butter. Mix in the bell pepper, onion, and garlic and saute for 5 minutes. Stir in the flour and sugar and cook for 1 minute. Stir in the wine, vinegar, and water. Mix in the soy sauce, ketchup, and black pepper. Reduce heat to low and let simmer for 5 minutes, or until the sauce has thickened. Return the pork pieces to the skillet and stir until well combined.