Peel 2 1/2 pounds Russet potatoes and cut into 3/4-inch cubes. Place potatoes in a large saucepan or pot and add cold water to cover by 1 inch. Add 1 tablespoon salt and bring to a boil. Once boiling, cook until fork tender, about 8 to 10 minutes.
Drain well and transfer the potatoes to a large bowl. Drizzle with 2 tablespoons distilled white vinegar and use a rubber spatula to toss gently until combined. Let cool for about 20 minutes while you prepare the rest of the ingredients.
Heat 2 tablespoons vegetable oil in a skillet over high heat. Add 2 cups frozen corn and cook without stirring for 2–3 minutes, then stir and cook another 2–3 minutes until some kernels are charred. Remove from heat and cool.
In a small mixing bowl, stir together 1/2 cup mayonnaise, 1/2 cup sour cream, 2 tablespoons lime juice, 1 teaspoon chili powder, 1/2 teaspoon garlic powder, and 1/2 teaspoon salt until combined.
Pour the dressing over the slightly cooled potatoes. Add the charred corn and toss gently to combine.
Cover and chill for at least 1 hour before serving.
Just before serving, stir in 1/4 cup chopped fresh cilantro, 1/4 cup sliced green onion, and 1/2 cup crumbled cotija cheeseGarnish with additional chili powder, cilantro, green onion, or lime juice if desired.