I don't even think the two plugs are exactly the same dimensions, so they likely wouldn't even fit; I recall the SNES having a fatter plug.
But beyond that, there's electrical incompatibility; beyond just that the SNES calls for +10v DC while the PS2's input is +8.5v, I do believe (though I could be mistaken) the PS2 is a more "modern" one that makes use of communication between the host and the PSU, whereas the SNES is entirely a "dumb" system. So in such a case, the PS2's power supply would fail to even power up, because the SNES wouldn't be capable of sending an "on" signal.