well,depends on wh made the unit,and then of course the one unit itself.
seasonic made would be a clear choice. thus buy a seasonic :)
and of course channel well tech can build good stuff,too!
ps yes,very paranoid. youll be pulling maybe 400 watts on the 12v fully clocked.
edit : look here
JonnyGURU.com - Thermaltake Toughpower Grand 1200W Review
and here
Uncomplicating the Complicated | Hardware Secrets
for overload tests
and here
techPowerUp! - The latest in hardware and gaming
since the greek guy(cmarris) knows his sheet :)