Maybe I should have been more clear (I know perfectly well how a SMPS works since after all I have designed quite a few myself, including with more sophisticated stuff like PFC); I was replying to a post that suggested that there was a significant difference in a AC/DC SMPS and a DC/DC SMPS when they are really the same thing except for a rectifier (which may be present in DC anyway since it eliminates polarity issues, but having hard-wired power installed by electricians would avoid problems, eliminating the ~1% efficiency loss; of course, the centralized power supply would still take in AC and you would have losses there).