Place potatoes in a large pot, cover with cold water, and salt the water. Bring to a boil, then reduce heat and simmer for 12-15 minutes until tender. Drain, let steam dry, and spread on a baking sheet to cool slightly.

Cook bacon in a skillet over medium heat for 6-8 minutes until crisp. Drain on paper towels, then chop into pieces.

In a large bowl, whisk together sour cream, mayonnaise, garlic powder, salt, and pepper. Stir in most of the green onions and three-quarters of the bacon if desired.

Add the warm potatoes and cheddar to the bowl and fold gently until evenly coated. Let stand 10 minutes, then fold again.

Transfer to a serving bowl, top with the remaining bacon and green onions, and serve right away or chill.