Gecko is a good resource, as it's written by people who actually understand how drives work, and the principles.

1/3 is probably OK if you're not pushing the motors to their maximum speed with high acceleration.
125% is most definitely a figure thought up by somebody who doesn't understand the power requirements of a stepper motor.

My preference is for a basic unregulated supply, with a transformer, rectifier and diode, however I normally used drives that use a basic DC input and dump energy back into the supply under decelleration. If you're using drives that accept a DC or AC input, then they don't do that (the drive input is rectified, so can't physically dump energy back out it), and I'd pick whatever power supply will physically fit better.