Power Supply Question, re Stepper Drivers

Hello

This is more of an electronics question, than a metalworking
question, but I'm sure no one will object.

I have Dan Mauch's 3 axis, 5 amp boards done and ready to hook up to
power and stepper motors. The logic part of the boards is 5V, so I'll
just buy a small wall "wart" from Radio Shack for that.

But it's the high power section that has me a bit concerned, because
I keep hearing that, for example, if you have a transformer with
115VAC primary, and 24VAC secondary, then pass it through a bridge
rectifier and a 15,000 uf capacitor, you'll end up with 36VDC.

Am I missing something? (probably!) How can you end up with a higher
DC output (36VDC)once you rectify and filter the AC output (24VAC)?
I thought if anything, the capacitor would bring the average voltage
down a bit (not up) and just provide a nice smooth 20 volts DC or so,
from a 24 VAC output.

I had my sights set on a toroidal transformer from a company in
Toronto, that outputs about 38 volts AC and 20 amps. Am I going to
wind up with 50 volts DC once it's rectified and filtered? That would
fry Dan Mauch's boards, I think. In the end, I want to end up with 36
to 38 VDC, about 20 amps, so what should my output VAC be from the
transformer?
Thanks to all those who set me straight on this. Cheers, Tom Kay.