1) Place the cut potatoes in a 3 quart saucepan and cover with cold water. Add 1 tablespoon salt and set over high heat. Bring to a boil, reduce heat to medium and simmer just until the potatoes are tender. Immediately remove the potatoes from the heat and drain in a colander. Rinse the potatoes under cold running water for 1 minute. Allow to drain well; Place potatoes on a kitchen towel to absorb the extra moisture.
2) Place the cooled potatoes in a large bowl. Add the capers, oregano, and onion. Place the vinegar in a small bowl, add a large pinch of salt and a few grinds of pepper, stir to combine. Add the olive oil and whisk to combine. Add the dressing to the potatoes and toss to coat. Season with additional salt and pepper. Allow to sit for 1 hour before serving.