1. Place potatoes in a large pot and cover with water. Bring to a boil over high heat, then reduce heat to medium and cook until tender, about 15 minutes. Drain and let cool.
2. In a large mixing bowl, combine mayonnaise, dill pickle relish, yellow mustard, salt, and black pepper.
3. Add cooled potatoes, celery, and green onions to the bowl. Stir gently to combine.
4. Cover and refrigerate for at least 1 hour before serving.