in the original stories his powers were down to his molecular density and low gravity as Krypton's high gravity not only means he is stronger here, his body is far more dense - it also means he is heavy
The yellow sun radiation bit was added around the late 70s, it was gravity plus yellow sun - it was much later the became, or seemed to be, the sole reason for the powers
under a red sun, on a planet with low gravity he would have strength and be heavier and denser, also indestructible
maybe without yellow sun he wouldn't be able to fly or have heat and x ray vision, but the other powers would be there
Faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings in a single bound - these would all still be there due to the gravity
presumably there would still be super speed, able to run fast, if not fly
Like John Carter, when he went to Mars he was strong and could jump high, due to the lower gravity
