Somehow manager to forget all my power electronics in like three months sorry. That voltage doubler is for an AC in and provides a DC out, which explains why when i first wrote that i was trying to figure out why it didn't need a boost converter to increase the voltage. That won't actually work since it is a DC input signal sorry.
There is an alternative option though, if we ignore trying to do it from a 12 V line on an ATX PSU and instead opt for a $15 PSU built for the purpose!http://www.circuitspecialists.com/24-volt-1-amp-power-supply.html
It isn't exactly the safest one if you are going to have it in an exposed area due to how the connectors are, but it will get the job done. I would put it in a secured area where things won't fall on it but it will have some room to breath.