Place cubed potatoes into a large kettle and cover with water. Bring to a boil over medium-high heat, then reduce heat to medium-low, cover, and simmer until the potatoes are just tender, 15 to 20 minutes.
Drain and spread the potatoes onto baking sheets in a single layer. Chill the potatoes in the refrigerator until cold, about 2 hours.
Mix the cooled potatoes, red onion, egg, mayonnaise, barbeque sauce, garlic powder, salt, and pepper in a large bowl.
