Place the cubed potatoes in a large pot of cold salted water. Bring to a boil. Cook potatoes until they are fork tender. Drain in a colander and let cool.
In a small bowl, whisk together mayonnaise, mustard, apple cider vinegar, sugar, salt and pepper.
Once cool, add potatoes to a large bowl. Add chopped onions, celery, and garlic. Pour the dressing over the potatoes and mix well. Season with salt and pepper, if needed.