Bring a large pot of water to a boil over high heat. Add the potatoes and cook until they are tender, about 20 minutes. Drain and quarter the potatoes then set aside in a large mixing bowl.
Set a large sauté pan over medium heat and add the bacon. Cook until the fat has rendered and the bacon is golden brown and crispy. Use a slotted spoon to remove the bacon to a paper towel-lined plate to drain.
Leave about 2 tablespoons of bacon fat in the pan and discard the rest or reserve for another use. Return the pan to heat and add the onion and celery, sautéing until tender and translucent, about 6 minutes. Set aside.
In a small bowl whisk together the vinegar, Dijon, salt, sugar and garlic powder.
Add the cooked onions and celery, bacon and parsley to the potatoes. Pour the dressing over the potatoes and toss to combine. Serve warm.