Try this link:
http://alas.ifrance.com/atlas/atlas2...er-supply.html
It relates to using the PC supply to power an amateur HF transceiver but your battery chargers can be about the same load.
It shows how to add a resistor (10K - 20K ohm) between two pins on the PWM chip to raise output voltage to 14 volts or more, without using the 5 to 10 ohm resistor on the 5 volt line.
Not for the faint of heart or weak at miniature soldering crowd.
It really does work too!