Now that I know my motor and drive choices, my thoughts have rushed ahead to the PSU for the drives. This is all speculative, but I wanted to air my thoughts.

We have 2x 4.2A Max steppers, and 2x 4.0A Max steppers. Thats a load of 16.4A at full pelt, but the drivers only need 60-70% of that current. So worst case, I need between 9.9 and 11.4A. Lets call it 12A for the sake of overbuilding things.

The highest inductance of my motors is 3.2mH. So, 32*sqrt(3.2) = 57.2V Ideal voltage. Drivers can take up to 80V.

The secondary voltage of an unregulated PSU is increased by the capacitor bank by a factor of sqrt(2) - So I'm aiming for an ideal secondary voltage of 41V.

12 A * 41 V = 492VA. This is the minimum power of transformer I'll need. Standard size options are therefore a 500VA transformer, or a 625VA transformer would be the next size up. Standard secondary voltages in my range are 2x25V (in Series = 50V), 2x40V (in parallel) or 2x45V (in parallel). I'm therefore looking at a 500 or 625VA transformer with 2x45V secondaries, giving a voltage to the drives of 64V.

Capacitors wise, to achieve a 5V ripple at 50Hz under full load (which keeps me above the ideal supply voltage) I'm looking at C = 12A / (4*50Hz*5V) = 12,000uF. But more won't hurt. Also, while we're talking capacitors, I ideally want them to be able to cope with 2x V (so 120V), but 100V rated caps will probably do the job.