On Sat, 07 Feb 2009 18:49:25 -0500, Phisherman wrote:
On Sat, 07 Feb 2009 17:23:32 -0600, Matt
wrote:

Suppose I have a plug-in transformer that reduces 120VAC power to some
lower AC voltage (say 12VAC or 24VAC), and suppose I want to do the
reverse---increase a low-voltage source back up to 120VAC.

Would there be a problem in connecting the low-voltage power to the
plug-in prongs of the wall wart (instead of the normal use: plugging the
prongs into the wall outlet) and expecting to get high-voltage power
back out the other end?

I guess my question is answered if I know that there are no components
other than the transformer inside the wall wart.

My immediate need is to use a 24VCT (center-tapped, 3-wire, 12VAC or
24VAC) to convert 24VAC back up to 120VAC.

If you do as you say, you'll get 1.2 volts output. You need a step up
transformer.

He'd get 120vac because he'd connect the 24VAC to the 24VAC side.
The problem is going to be loses and power considerations. He'll be lucky
if he ends up with enough power to run a clock.