Wash the potatoes and scrub if necessary. Put them in a large pot and cover with water by 2 inches. Boil whole, with skin on, until they can easily be pierced with a sharp knife, about 20-30 minutes depending on their size.
Drain the potatoes, and while still hot, cut them into bite sized pieces and place in a heatproof bowl. Pour the vinegar over the potatoes and add 1 teaspoon of salt and toss to coat. Let cool slightly while you prepare the other ingredients.
Add the mustard, olive oil, celery, and chopped sun dried tomatoes. At this point you can cover and refrigerate the salad up to a day ahead.
Before serving, toss in the dill and chopped scallions. Taste for seasoning. Potatoes can absorb a lot of seasoning, so you may need up to another teaspoon of salt,a few more splashes of vinegar, or more oil if it seems too dry.