Place potatoes in a 6-qt. stockpot; add water to cover. Bring to a boil. Reduce heat; cook, uncovered, just until potatoes are tender, about 15 minutes. Drain; cool slightly., In a large skillet, cook bacon over medium heat until crisp, stirring occasionally. Using a slotted spoon, remove bacon to paper towels, reserving 3 tablespoons drippings., For dressing, saute onion in drippings over medium-high heat until tender, 4-6 minutes. Stir in flour until blended. Stir in sugars, salt and pepper. Gradually stir in vinegar and water; bring to a boil, stirring constantly. Cook and stir until slightly thickened, 4-6 minutes., Slice potatoes; place in a greased 5- or 6-qt. slow cooker. Top with dressing; sprinkle with bacon. Cook, covered, on low until heated through, 3-4 hours. If desired, sprinkle with chives.