Gecko recommends a simple unregulated power supply for their drivers. This is made up of a power transformer, a bridge rectifier, and a filter capacitor. You would think that simple power supplies are easier to find than elegant regulated supplies, but that's not the case. If you want a simple power supply, you'll probably have to make your own (that's what I did).

However, other companies making stepper motor drivers provide a traditional regulated power supply. Who's right? I don't really know. If I did it again, I would probably buy a cheap regulated power supply from Interinar or from eBay.

When calculating the voltage of your power supply, follow Gecko's guideline for voltage, but of course stay safely below the maximum rated voltage of your driver. Likewise, for determining total power supply current, follow Gecko's guideline and allow a reasonable margin of safety above that.