My power supply calculations and a zener question

I'm trying to figure out a power supply to use with a three axis
A3977 based driver. I read the Gecko white paper and its pretty
straight forward.

Anyway, The A3977 can handle 35 volts at 2.5A for each driver - 7.5A
total. While I'm not planning on adding a fourth axis, just in case
I'll add on another 2.5A - 10 AMP minimum. So I want the power
supply to be able to handle at least 12A to give me a little room.

Unfortunately the 35V includes back EMF so the limit is really about
30V

If I use a 22VAC transformer, that'll give me about 30.8 VDC out.

The bridge is a no-brainer but the cap takes a little math

Using the Gecko capacitor formula, I should use at least a

C = 80,000 * 12 / 30.8 = ~31,000 uF
V=Vin+Vin*0.2 = ~37v

Closest I can find is 33,000uF @ 50v Electrolytic

The only thing I'm not sure about is what they say about protecting
the cap from back-emf voltages when voltage is near the voltage
rating of the drive. Since we run all these motors at 5-20 times
their voltage ratings, isn't this always a requirement?

Since I can't exceed 35 volts on the A3977, a 33 volt zener should
do the trick. Above my desired voltage but below the A3977's limits
But what power rating do I need? The whole 12 Amps? If so this could
be tough, 5W is the highest Digikey has.