First, I'd dismantle the SNES and check if any resistors or other parts on the PCB are fried (see if they're black or something). If everything seems alright, I'd try a PAL SNES power supply. With it, your WildCart (in case you have one) won't work, but you can see if your SNES works. Check BOTH polarities. The NTSC SNES has a diode in it that will prevent it from blowing up if the polarity is wrong.
If nothing works, just trash your SNES. There're plenty of them on eBay. I recently got one (my second US SNES :) for US-$20. Nice, huh?
-Cyan