It seem you fried your usb hub because you switched the polarity.
On any STANDARD USB port, it's made to provide 5 volts at 500mA = 2.5 watt each. Some laptops will power more (my Shuttle SFF provides less). From my understanding you are looking for a 12V to 5V converter that will provide 2.6A...correct? why don't you use the 5V from your PSU?