This component carries the markings SMS5408 0932 is busted! It is part of a 1000W psu of a flagship subwoofer of a (very) respectable brand, and I can't find any datasheet at all for it!
I assume it is a MOSFET because of the G,D and S markings on PCB. Only thing I could find for the SMS was this company:
that seems to provide asic services, doesn't seem to manufacture components. Also couldn't find any reference for 5408 except diodes.
Usual websites like alldatasheet, datasheetcatalog, etc didn't bring anything up. Contacting the manufacturer is no good, they've sent me another unit so no one would have to worry about repairing anything. But I really won't let this off because I can't find a replacing mosfet!! ;)
New image (PCB backside):