In a large saucepan combine potatoes with salted water to cover by 1 inch and simmer until just tender, about 20 minutes.
While potatoes are cooking, in a medium heavy skillet cook bacon over moderate heat, stirring, until browned and crisp and transfer with a slotted spoon to paper towels to drain.
Drain potatoes and let stand until cool enough to handle. Cut potatoes into eighths and in a bowl combine with bacon. Keep mixture warm, covered.
Pour off all but 2 tablespoons fat from skillet and saute onion over moderately high heat, stirring, until softened, about 3 minutes. Add sugar, 1 tablespoon vinegar, and broth and simmer 2 minutes. Add onion mixture to warm potatoes with parsley and remaining 1 tablespoon vinegar, tossing gently, and season with salt and pepper.
Serve potato salad warm or at room temperature, garnished with parsley.