Bring a large pot of water to a boil, add the russet potatoes, and cook until tender, about 15–20 minutes, until a knife slides in easily. Drain the potatoes and spread them on a sheet pan to cool completely, about 10–15 minutes, with visible steaming stopped before mixing.

Chop the hard-boiled eggs, dice the celery, and finely dice the onion. Combine the cooled potatoes, chopped hard-boiled eggs, diced celery, finely diced onion, and sweet pickle relish in a large bowl until evenly distributed.

In a bowl, whisk mayonnaise, yellow mustard, white vinegar, sugar, salt, and pepper until smooth and creamy. Stop when the dressing looks uniform with no sugar specks visible.

Pour the dressing over the potato mixture and fold gently until the potatoes look coated. Refrigerate for at least 3 hours (3–4 hours) until the salad is cold and holds together when spooned.

Before serving, garnish with paprika in a light dusting over the top. Serve cold and keep the surface covered to prevent drying.