Tb6600?

[Neale]

If you are using the common switch-mode power supplies (these are generally contained in a single box, lighter weight, and cheaper) then it is very important not to exceed the rated current. If you do, you trip the over-current protection mechanisms, the PSU shuts down temporarily, and things can go wrong. I don't think I've seen kits with multiple PSUs but it's probably to make sure that there is enough current capability. The stepper drivers actually draw current as a series of relatively short pulses; if your three drivers all demand a pulse at the same time then the sun of these might be too much for the PSU. No reason not to use a single supply as long as it can handle the peak current.

A better technical solution is to use a so-called linear power supply. Heavier and a bit more expensive but easy to build yourself from available components (plenty of examples on this forum). The advantage is that they can be rated for the average current draw and can deal with short pulse loads without a problem.

I would disagree with Gerry about voltage and torque. Stepper motors are driven by short pulses. When a pulse begins the current in the motor winding starts to rise, ramping up to its maximum. The higher the supply voltage, the faster the current rises and as it's current that translates into torque, the quicker the torque is developed during the pulse. The overall effect is higher average torque, which helps acceleration. Highest voltage that the driver can stand will give the best overall performance.