Place the cubed red potatoes in a large pot and cover with cold water, adding 1 tablespoon of salt to the water.
Bring the potatoes to a boil over medium-high heat, then reduce to a simmer and cook until fork-tender, about 10-12 minutes.
Drain the potatoes thoroughly in a colander and allow them to cool completely.
In a large mixing bowl, combine the Hellmann's mayonnaise, Dijon mustard, and sweet pickle relish, stirring until smooth.
Add the finely diced celery and red onion to the dressing mixture and stir until evenly distributed.
Once the potatoes have cooled completely, gently fold them into the dressing mixture using a rubber spatula.
Season with salt and freshly ground black pepper to taste. If using optional ingredients like hard-boiled eggs or herbs, fold them in now.
Transfer the potato salad to a serving bowl and sprinkle the top with paprika.
Cover and refrigerate for at least 30 minutes before serving, though 2 hours is ideal to allow flavors to develop.
