Computer supplys for charger power question

[J57ltr]

Hey guys I have been using an atx power supply for years and it has worked fine until now. It always only put out about 11.8V. I am using a 10 ohm 5W resistor to load the 5V source.

Anyway it just died on me and I gave it a once over and just decided to use another since I have several. After a few that were no good I found a good one. I modified it to work but I still only get 11.88V. What is the proper way to increase the voltage to about 12.5?

Thanks

Jeff