Place the cubed potatoes in a large pot and cover with cold, salted water by about 1 inch. Bring to a boil over high heat.

Reduce heat and simmer until the potatoes are fork-tender but not mushy (about 15-20 minutes). Drain thoroughly and allow them to cool slightly for at least 10 minutes.

While the potatoes are cooking, prepare the dressing: In a large bowl, whisk together the mayonnaise, yellow mustard, sweet pickle relish, apple cider vinegar, and sugar until smooth.

Gently fold the slightly cooled potatoes, chopped hard-boiled eggs, celery, and red onion into the dressing mixture. Use a large spatula to avoid breaking up the potatoes too much.

Taste the salad and adjust seasoning with salt and freshly ground black pepper as needed. For best flavor, cover the potato salad and refrigerate for at least 2 hours before serving. This allows the flavors to meld.

Garnish with a sprinkle of paprika or chopped fresh parsley just before serving.