Does a camera flash gun require constant current or constant voltage?

A friend of mine is designing a power adapter to use with my Nikon SB900's in my studio. Capacity is 6volts 5 amps. He wants to know if i require Constant Current or Constant Voltage. Please don't advise me on using this kind of setup as I have weighed the pro and cons.

You'll need a reasonably stable "constant" voltage that can supply a small current just like a battery does. The flash involves quite a high current for a very short time; this is provided by a condenser inside the device.

Simply match OEM specs.IE… Graphics on inside cover of battery compartment that denotes "battery of cells" Which indicates polarity of that "battery of cells" when installed. Also displays type "cells used in battery", you would have mentioned other wise. That in and of itself gives voltage and current required.