Place the potatoes in a large pot of salted water and bring to a boil and cook for 20 to 25 minutes, until the potatoes are tender when pricked with a knife. Drain and cool the potatoes.
Meanwhile, in a large mixing bowl, combine the sour cream, mayonnaise, sweet pickle relish, mustard and celery.
When the potatoes are cool enough to handle, cut them into small, bite-sized pieces and add them to the bowl. Add the hard boiled egg and egg white and stir to combine. Season with salt and pepper. (This can be made in advance and stored in the refrigerator for 3 days.)
Just before serving, stir in the red onion. Transfer the potato salad to a serving bowl and sprinkle the paprika on top.