maybe a 5670 or 6670. neither one needs an external power connector and your little power supply shouldn't have problems running it.
under 12v...... how many amps ? 20 ?
I think the 12v has 14amps. the sticker looks like this
+12v / 14a
+5v / 25a
+3.3v / 18a
-12v / 0.8a
+5VSB / 2a
Thats what's on there.