Boil the elbow macaroni in well-salted water according to the package directions until al dente, then drain and rinse under cool water until completely cooled. The noodles should feel tender but still hold their shape, and they should no longer feel warm in the center.

Whisk the mayo, yellow mustard, white vinegar, black pepper, white sugar, salt, granulated garlic, and onion powder in a mixing bowl, then stir in the red onion, celery, and green bell pepper. The dressing should look smooth and creamy, with the vegetables evenly suspended and the aroma turning tangy and savory.

Transfer the cooled macaroni to a large bowl, add about half of the dressing, and toss gently to coat, then cover and refrigerate the pasta and the remaining dressing for at least 2 hours. The salad should look a little more dressed than you think it needs before chilling, because the pasta will absorb some of that moisture as it rests.

Just before serving, add the remaining dressing and fold until everything is evenly coated, then season with additional salt and pepper to taste. The finished salad should smell brighter after resting, and the texture should be creamy with crisp pops of celery and bell pepper.