Hi, Kaderick
If your using Gecko's or a Control Board with Current Setting Feature, Your power supply should be close to the max volt's for the control board/box.
Example: Gecko's are rated 80 volt's and up to 7 Amp's w/Heat-Sink, Current is set on the gecko, Limiting the Amp's to the rating of your Stepper Motor.
You don't really need to now the volt's with above type controls. Your motors after running for awhile should be hot enough that.
If you put your hand on it, You really feel the need to Turn it lose in 2-3 seconds, Pretty warm.
If you have a stepper, 2.5 Amp's, "X" 3 ohm's = 7.5 Volt's "Ohm's Law", The margin between 7.5 and 80 volt's is 26.666 times the volts you need.
This difference is used up as the stepper goes faster to maintain the Amp's at 2.5 until 80 volt's is reached, then the torque drops off.
That's where you start losing step's more or less, Some what simplified, Lot's on the Web to see on this.
Hope this Helps, Chip