Place the potatoes into a pot and fill it with enough water to cover them. Bring to a boil and cook for about 10 minutes, or until easily pierced with a fork. Immediately drain and set aside to cool slightly.
Using your preferred method, fry the bacon until browned and crisp. Reserve the bacon grease.
Combine the bacon grease and onion in a large skillet. Cook over medium heat until the onions are translucent and just starting to brown.
Add the apple cider vinegar, water, sugar, and celery salt to the pan. Bring to a boil and stir until the sugar is dissolved.
For warm potato salad: Add the potatoes and half of the bacon to the pan. Heat through, then transfer to a serving dish. Crumble the remaining bacon over the top and serve warm. Top with fresh or dried parsley if desired.
For cold potato salad: Pour the sauce and half of the bacon over the potatoes in a bowl. Stir to combine and refrigerate until ready to serve. Sprinkle the remaining bacon over the top before serving.