How many amps do the steppers draw? How many amps is the PS. Did you wire your drives in a daisy chain or star pattern. Daisy chain is where you wire one after another so one power line goes freom drive to drive, while star has each drive having it's own power wire leading to a central point. If daisy chained, the single wire cannot give enough amps for all then drives down line.
For total amperage needed from your PS, add up all motor amperage, then multiply by .66. Say each motor needs 3A. Withn four motors, that comes to 12A. Now multiply 12A by .66 and you get 7.92 amps needed. Round it up to 8 amps. Anything less and even if the drives are wired inn a star orientation, you will still be deficient in power to drive multiple drives at once.
Now for the ringer. It is doubtful you will ever run four drives at once. Most likely just three. If the Kelling drives will take 48v., I'd go with the 48v 7.2A power supply.