Yes that box is a PC PSU. I use that PSU to power my pump, I have a 12v DC diaphragm pump. Although it is only 12v DC it is a crazy 10 amps minimum.
Now for anyone that is wondering how I got it to power up with out a motherboard attached here is the trick. If you look at the long 20/24pin motherboard connector you will see a green wire. If you take that green wire and connect it to a black wire the PSU will power on as long as it is plugged in with the switch on.
You can check out this tutorial
here... This is also great for powering fans, I have several 120mm PC fans and out pushes 130CFM. You can even find 240mm fans now which would be great for circulating air.