Wash potatoes. Place in a pot with cold water and bring to a boil. Lower heat and simmer for about 20 minutes until potatoes are fairy easy to pierce. Strain in a colander. Let them cool off and then slice them (skin will come off easily). Place in a large bowl and set aside.
Make the dressing by mixing first the vinegar with the lemon juice, then whisk in the olive oil and at the end add the yogurt ,mixing until smooth.
Add the cherry tomatoes, cucumber, chopped parsley and onion to the potatoes and gently mix. Add the dressing and mix, making sure all the ingredients are covered with the dressing.
Cover and refrigerate for about 2 hours.
Before serving sprinkle with the capers.
Add salt and pepper as needed.