If using regular cucumbers, slice them in half lengthwise and use a spoon to scrape out the seeds. Thinly slice all cucumbers into 1/8-inch rounds.
Place cucumber slices in a colander and sprinkle with 1 teaspoon salt if desired. Let sit for 10 minutes to draw out excess moisture, then pat dry with paper towels.
In a medium bowl, whisk together sour cream, mayonnaise, white vinegar, fresh dill, garlic powder, onion powder, sugar, black pepper, and 1/4 teaspoon salt until smooth and well combined.
Add the cucumber slices (and red onion if using) to the dressing. Gently toss until all cucumber slices are evenly coated with the creamy dressing.
Transfer the salad to a serving bowl, cover, and refrigerate for at least 30 minutes before serving to allow flavors to meld.
Give the salad a gentle stir before serving. Taste and adjust seasoning with additional salt or pepper if needed.