To be honest, I don't see the evidence that he instantly loses all of his power under a Red Sun, not today.
Scott Lobdell had him slowly losing his powers when he returned to Krypton to stop H'el. Dan Jurgens had Superman stranded on an alien planet with Luthor early this year, and there he still retained residual power, for at least a time. And here in Dan Jurgens' latest return to Krypton Superman is still seen to take a laser bolt with only cosmetic damage... I find this treatment an agreeable take, my referred one at any rate, as with the superb Exile storyline in the late 1980s you can get terrific drama and tension from a Superman who is working off residual power only, and this story treatment is far better than him instantly losing everything. It would be a marvellous touch if Jurgens harks back to the dawn of the Golden-Age and has Superman with enough strength left to leap tall buildings on Krypton, but in truth few writers ever tackle or even acknowledge Krypton's enormous gravity and alien environment....
I would like to see DC official accept as canoin now that Superman always has some super powers left reagrdless if under a Yellow Sun, for due to gravity/mass of His homeworld, Kal shoudl have a baseline like say Siperman for speed/strenght, and have original Luke Cage steel hard skin!