The PS cannot put out more power than the demand for it but will have a limit to the maximum before it shuts down or damages itself. Yes, the OS can affect the demand for power. On my old dual OS PC, more power was consumed running Win 2k than XP...this having something to do with advanced power management but I don't know how that works. The motherboard will have some voltage regulation circuity as will the PS but power regulation is demand based. Motors, electronic circuits, etc. produce some power demands of their own but running processes from the OS and software increase that demand.
My PC is consuming more power than it used to and I haven't added/removed any hardware from it. I am running a different OS.