Bring a large pot of salted water to a boil. Add elbow macaroni and cook for 7-8 minutes until al dente. Drain and rinse under cold water.

In a mixing bowl, whisk together mayonnaise, yellow mustard, white vinegar, garlic powder, salt, pepper, and granulated sugar.

Chop red onion, celery, and green bell pepper. Stir into the dressing.

Combine the cooled pasta with half of the dressing and toss gently to coat.

Cover and refrigerate for at least 2 hours. Stir in remaining dressing before serving.

Taste and adjust seasoning with salt, pepper, or sugar if needed.