Bring potatoes to boil in large pot of water. Reduce heat to medium-low and simmer until potatoes are tender, about 17 minutes. Drain; let stand until cool enough to handle, about 20 minutes.

While potatoes are boiling, combine 1 tablespoon rice vinegars and remaining ingredients in a small bowl, set aside.

When potatoes have cooled, Cut into 3/4-inch pieces. Place 1 layer of potatoes in large bowl; sprinkle with 1 tablespoon of vinegar and salt and pepper. Continue layering potatoes with vinegar, salt, and pepper. Add dressing and toss. Season with salt and pepper.

DO AHEAD Can be made 8 hours ahead. Cover and chill.