In a small bowl whisk together vegetable oil, vinegar, sugar, salt & pepper. You can use a glass jar with lid to mix the dressing. Set this aside so favors will marry.
In a large pot, put the pototoes in water to boil until fork tender. Drain & set aside until they are cool enough to handle. Peel and cube or slice into bite size pieces.
Next, peel & thinly slice the onion. I love to use 1015Y's or Walla Walla. You can also use green onions, too for color. A combination of both is fine. Place the onions on top of the potatoes & mix
Blend the dressing well & pour over the pototoes. Take a taste to see if you need more seasoning. You can use any combination of oils or vinegars. I have used olive & wine vinegar. So you might need to adjust sugar, salt or pepper.
I have an aunt that will put leftover cooked bacon, ham or pepperoni in this as well. Place salad in refrigerator until ready to serve. Mix well. If you want more dressing remember to use equal parts oil to vinegar. Enjoy!