boil potatoes, drain and rinse with cold water. Cut into 1/2-inch cubes and set aside in large bowl. Add the diced hard-boiled egg whites to the potatoes along with the onions, celery, mayonnaise, mustard, relish and garlic powder. Toss well. Season to taste with salt and pepper. Refrigerate for at least 2 hours before serving. Makes 4 cups.