Increase voltage output by connecting 2 PSU channels together
It is highly doubtful if that supply has three separate outputs. Take an ohm meter and with the supply OFF measure resistance between each of the V+, V+ and V+ pins. I suspect that you will find them all bussed together.

Likewise use the ohm meter to measure resistance between the COM, COM and COM terminals. I suspect that you will find all three bussed together. 

I give a strong indication of this being a single output supply because I zoomed in on the eBay picture that you pointed to and peeked through the screen cover. I could not see circuitry that would suggest a triple output unit.