While still warm, sprinkle red wine vinegar evenly over drained potatoes, & mix well. Let stand for 20 minutes - the potatoes will soak up the vinegar. In a blender, combine mayonnaise, sour cream, yolks from hard-boiled eggs, mustard, garlic powder, onion powder, salt & pepper.
Most potato salads look and taste better when made with low-starch red boiling potatoes. For Classic American-Style Potato Salad, you can use any size of this variety, but the small new potatoes cook 10 to 15 minutes faster than the larger ones. Choose potatoes that are all roughly the same size, if possible, so they cook in the same time.