Put the potatoes in a medium-size saucepan and cover with cold water; add 1 teaspoon of the salt. Bring to a boil, then reduce the heat to medium and cook until fork tender, about 15 minutes. Meanwhile, saute the bacon in a skillet over medium-low heat until crispy, about 12 minutes.
Drain the potatoes (do not rinse), transfer to a baking sheet and let cool for 6 to 8 minutes, then cut into quarters.
In a bowl large enough to mix the potatoes, combine the vinegar, yogurt, mustard, scallions, red onion, sugar, remaining 1/4 teaspoon of salt and pepper. Transfer the potatoes to the bowl, add the bacon and hard-boiled eggs and mix by folding carefully. Serve at room temperature.