Place the cubed potatoes in a large pot and cover them with cold, generously salted water. Starting the potatoes in cold water helps them cook more evenly from the outside toward the center.

Bring the pot to a boil, then reduce the heat to a steady simmer. Cook for approximately 10–15 minutes, checking often, until the potatoes are fork-tender but still firm enough to hold their shape.

Drain the potatoes well and spread them in a large bowl or on a baking sheet to release excess steam. Let them cool for 10–15 minutes so the dressing stays creamy rather than becoming oily or thin.

While the potatoes cook or cool, cook the bacon until crisp, which takes about 10 minutes depending on the method used. Drain it, let it cool, and crumble it into small pieces.

In a large mixing bowl, whisk together the mayonnaise, sour cream, kosher salt, black pepper, and garlic powder if using. Taste the dressing and adjust only after considering that the bacon and cheddar will also add salt.

Add the cooled potatoes, about three-quarters of the bacon, most of the cheddar, and the green onions to the dressing. Fold gently with a spatula until the potatoes are coated without crushing the cubes.

Cover the bowl and refrigerate the potato salad for at least 1 hour, although 2–4 hours gives the flavors more time to mingle. Keep it chilled while it rests.

Before serving, garnish the salad with the reserved cheddar, bacon, and green onions, adding chopped parsley or extra chives if desired. Taste once more and adjust the seasoning if needed, remembering that cold food can taste less salty.