You definitely need a DC power supply, the Rutex/Gecko drives will not convert AC to DC.
The size of the PS is determined by the motors you are using and by the max volts/amps the Rutex drives will allow.
Some have luck with standard regulated/switching power supplies. These can get expensive when you look at 24V 10A (probably a minimum even with small servos) - 70V 25A+ (or more if driving large servos) power supplies.
Alot of people build their own, unregulated power supplies. This basically consists of a (sized for your application) transformer to step down the 120VAC to your required DC voltage range. Then a properly sized bridge rectifier to convert the stepped down AC from the transformer to ripply DC. Then a large 100V+ 10,000ufd+ capacitor to remove the ripple and give filtered DC, and backup for surges. Of course you do all the wiring, so electrical knowledge is a plus, considering the danger of messing with 120VAC. On the other hand, you can build exactly the sized PS that you need for your application. It will end up being cheaper/better performing than comercial regulated power supplies, assuming you can even find a comercial power supply with the outputs you need.
Check out http://www.plitron.com/ for toroidal transformers wound for various outputs. Also they have a schematic for what I'm describing in their 'TECH NOTES' section under 'full wave bridge'.
Check out http://www.campbelldesigns.com/ for a small tutorial on how to design/build a power supply like I'm describing.
Check out the CAD CAM EDM DRO Yahoo group in the files section. There is a schematic and part#'s for a PS in the 'circuits' section under "Jerry's power supply."
Finally, search around these same forums, there are other's looking for the same.