Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and let cool.
Mix yogurt, mayonnaise, mustard, sherry, pickle juice, salt, and pepper together to make dressing.
Halve or quarter potatoes and place in a bowl. Add celery, green onions, and pickles. Spoon in dressing and toss to combine.