Cook potatoes in enough boiling salted water to cover for 15 minutes or until tender; drain and cool.
In a small bowl, combine chili powder, sugar and 1/4 teaspoon of salt.
Rinse salmon, pat dry, rub chili powder mixture into it and place it on the greased rack of an uncovered grill over medium heat.
Grill for 4 to 6 minutes per 1/2-inch of thickness or until fish flakes easily when tested with a fork, turning once.
Cool salmon slightly then break it into chunks. In a medium bowl, stir together salsa, lime juice and remaining salt.
Add potatoes, salmon, green onions and cilantro; toss gently. Divide mixture evenly among warmed tortillas; top with sour cream and enjoy!