Add the potatoes to a large saucepan of cold water. Bring up to a boil, add a nice handful of salt and reduce to a simmer. Cook until tender, about 20 minutes. Drain and cool.
Add the potatoes, celery and onions to a large bowl. Whisk together the mayonnaise, mustard, relish, sugar, smoked paprika and some salt and pepper in a separate bowl. Fold the dressing into the potatoes. Cover with plastic wrap and place in the fridge for at least 3 hours so the flavors can marry.