Place potatoes in a saucepan, and cover with water. Bring to a boil. Reduce heat; simmer 15 minutes or until tender. Drain. Cool slightly and peel. Cut potatoes in half lengthwise; cut halves crosswise into 1/4-inch-thick slices. Place potatoes in a large bowl; sprinkle with vinegar.
Combine yogurt and sour cream in a medium bowl, stirring with a whisk until smooth. Add oil; stir with a whisk. Add onion and remaining ingredients; stir with a whisk. Add yogurt mixture to potato mixture; toss gently to coat. Cover and chill 1 to 24 hours.