The PW-200M doesn't have wide input voltage support (it accepts between 11v and 14v) and also the +12v rail isn't regulated. The regulation is recommended because of that +12v rail and because devices that use might not like when it goes too high. If you are using a mini-itx board and laptop hdds / slim cdroms, then these devices usually don't use the 12v rail but only the 5v one .
