In a medium bowl, combine the mayonnaise, sour cream, white vinegar, granulated sugar, celery salt, Dijon mustard, onion powder, and black pepper. Whisk together until smooth.

In a large bowl, add the coleslaw mix or homemade shredded cabbage and carrots. Break apart clumps for even distribution.

Pour the dressing over the coleslaw mix and gently toss to coat the vegetables evenly.

Cover and chill in the refrigerator for at least 1 hour to allow flavors to meld. Serve immediately if short on time.

Before serving, stir the coleslaw well and adjust seasoning with salt or pepper as needed.