To make dressing: Whisk sugar into vinegar until it dissolves. In a mini-processor, zap all the dressing ingredients (including the sweetened vinegar) until a creamy dressing is formed. (make sure garlic has been pulverized).
Put all the potato salad ingredients into a bowl. Pour dressing over and combine to coat evenly. Season to taste with salt and pepper. Refrigerate 2-3 hours before serving to allow flavours to blend.