Well, for starters you need more than just a stable +12V output to get a computer running, you need
+12V, +5V, +3.3V, -5V, -12V, +5V(standby)
Additionally 13.2V 3A is only 39.6W which is not enough to power any system that has a decent processor in it. This would be borderline for powering a mini-ITX system as well. Keep in mind that even if the power requirements are lower than 40W, inrush startup current can nearly double the required power for starting the system which can easily exceed 40W.
And at a price of $83USD that's quite hefty just for an intermediate power converter. You'd probably need 2 of those in order to get enough power, and then you still have to worry about downgrading the voltages to the required ones.
Computer voltage levels tend to have around a +/-10% tolerance max, so +13.2V on a +12V rail would be ... borderline and not recommended.