In a medium bowl, whisk the mayonnaise, yellow or Dijon mustard, and 1 tablespoon of granulated sugar well. Set aside.
Scrub potatoes well and peel. Dice the potatoes into 1 inch chunks.
Place diced potatoes into a large stock pot with enough water to cover them. Add 1/4 cup salt and 1/4 cup granulated sugar to the water and boil until you can easily poke into the potatoes with a fork or pairing knife.
Drain potatoes into a colander. Using a slotted spoon, scoop out about 1/3 of the potatoes and pass through a ricer. If you do not have a ricer, use a potato masher and gently break up the potatoes. You want fluffy versus mashed.
In a large bowl, combine all of the potatoes, chopped boiled eggs, diced onion, celery, and pimentos. Add the relishes.
Pour the dressing over the potato mixture and using a rubber spatula, mix the entire bowl of ingredients until very well combined, making sure to scrape down the sides of the bowl. Add salt and pepper to taste. Add additional relish if necessary after tasting.
Cover with plastic and refrigerate for a minimum of 2 hours. Stir well before serving. Dust with chopped celery leaves and paprika if desired.