Some people seem to be confused as to how Superman 1M, and the rest of the Dynasty were being powered, I thought it was obvious.
They were powered by the Super-Sun of their time. Thats why when S1M went back to the past, even though he was still under a yellow Sun, he was still losing his powers.
Superman Prime made it so the Dynasty would have these massive powers, but only under the Super-Sun which Prime empowered.
So IMO Supes Prime wasn't just chillin in the Sun, and every time a new Superman popped up he said "ok time to power that guy up!". 😂
Once the new Superman was born, the Super-Sun gave them their powers, just as the regular Sun gave to our Superman, but to a much greater degree.