Bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook according to package directions until al dente (about 8-10 minutes). Drain thoroughly in a colander and rinse with cold water to stop the cooking and cool the pasta. Let it drain very well, shaking the colander to remove excess water.

While the pasta cooks and cools, prepare the dressing. In a large mixing bowl, whisk together the mayonnaise, sour cream, white vinegar, Dijon mustard, granulated sugar, garlic powder, fresh dill, black pepper, and salt until smooth and well combined. Taste and adjust seasoning as needed.

Add the cooled and well-drained pasta to the bowl with the dressing. Add the finely diced celery, red onion, bell pepper, and drained sweet pickle relish. If using, add the chopped hard-boiled eggs.

Gently fold all ingredients together with a rubber spatula until the pasta and vegetables are evenly coated with the creamy dressing.

Cover the bowl tightly with plastic wrap and refrigerate for at least 1 hour, or preferably 2-4 hours, to allow the flavors to meld and the salad to chill thoroughly.

Before serving, give the salad a good stir. If it seems too thick, you can add a splash of milk or a little more mayonnaise (1-2 tablespoons) to reach your desired consistency. Serve cold.