Voltage Doubler

I'm an "old" (57) El.Engineer. Due to this lot of "past years", I'm not able to find a good, reasonable and efficient solution to this problem. I've a PC power supply (500W), wich provides 12V/39A and 5V/20A (and others...) outputs. I would like to realize a lab power supply for numbers of IT micro peripherals (powered with 5V mini-USB supplies, you see?), without to have a lot of chargers... (e.g. Raspberri Pi's), but also other equipments who need 12V power (Arduino...). That's why I choosed this "PC power" solution (and without problem ;-). But, seeing the power of this "large" supply, I would like to be also able to have a 24V power output. In theory, it exists a system called "pump charge transfer" (or smthg like that), using commutation of condensators, parallel then serial (parallel charge with 12V, then serial discharge: 12+12=24...). Fine, but how can it be realized??? As said above, my "old" memory (and capacities :-) are also quite "discharged" for finding a solution to this problem. Can anybody help me? Thanks a lot. As said above, the power supply also delivers 5V; it may be added to rise to a sufficient voltage for e.g. a 7824 regulator.... And finally, a 24V/2A output will be enough. Best regards from Brussels, Belgium