Kerry Wong wrote a post on his blog showing how he modified the 12V rail of a TL494 based ATX power supply to 14.6V for 4S LiFePO4 battery charging:
To charge the 110Ah battery bank I built, I need a power supply that can provide at least 10A at 14.6V. Since I have many old ATX power supplies lying around and the 12V rails of these power supplies are more than capable of providing 10A, I decided to modify one such power supply for using as a 4S LiFePO4 battery charger.
More details at his blog here.
Check out the video after the break.