1. In a heavy 12-inch skillet combine the sugar, 1 teaspoon of the salt and the black pepper in 2 cups of water. Then drop in the potatoes and apples and bring the water to a boil over high heat.
2. Reduce the heat to moderate and cover the skillet tightly. Simmer, undisturbed, until the potatoes are tender bUt not falling apart.
3. Meanwhile, in an 8- to 10-inch skillet, cook the bacon over moderate heat until brown and crisp. With a slotted spoon, spread it out on a double thickness of paper towels to drain.
4. Add the onions to the fat remaining in the skillet and cook over moderate heat, stirring frequently, for 8 to 10 minutes, or until the rings are soft and light brown.
5. Just before serving, stir the remaining teaspoon of salt and the teaspoon of vinegar into the potatoes and apples, and taste for seasoning. Then transfer the entire contents of the skillet to a heated bowl and serve topped with the onion rings and bacon.
