On the PlayStation 3 secrets page it stated that the ZSSR5391A power supply was only included in the earliest batch of PS3s. I can confirm that isn't true. I recently opened up my 60GB PS3 system manufactured on Feb 2007 (apparently one month before that model ceased production), and that included the ZSSR5391A power supply.
I have replaced it with the APS-231 and my PS3 runs much cooler.
