Bring a large pot of water to a boil, then add the cubed russet potatoes and cook until tender, 10 to 15 minutes with visible simmering bubbles. Drain and spread the potatoes on a sheet pan to cool completely, about 15 to 20 minutes, until no steam rises.

In a large bowl, combine cooled potatoes, chopped hard-boiled eggs, diced celery, finely diced onion, and sweet pickle relish. Fold gently until the mix looks evenly speckled with eggs and relish.

In a separate bowl, whisk mayonnaise, yellow mustard, white vinegar, sugar, salt, and black pepper until smooth and glossy. The dressing should pour easily and look uniform in color.

Pour the dressing over the potato mixture and fold gently until everything is coated, 1 to 2 minutes, with no dry potato pockets. The salad should look creamy and cohesive.

Refrigerate covered for at least 3 hours to let the flavors meld, keeping the texture thick and creamy. For best results, chill until cold throughout, with no warmth in the center.

Just before serving, garnish the top with paprika for a classic speckled finish and a brighter surface color. Serve chilled with the creamy layers visible in the bowl.