Sara,
Wall wart power supplies are not dimmable.

You might want to shop around for dimmable transformers which cost less.

David, I just keep thinking somehow there is a way to get around it:-)

Do you know whether a wall wart adaptor powering LED UCL meet the code or not? ing

BTW, I have searched for dimmable transformer, they are all in the range of $80-100

Sara,

You need to check with your local authority, but I think it depends on how the lights are setup.

If you installed the environmental lights 3 pin lights, they have a stub dimming attachment you fit onto the end of a light bar. That way, you can run the lights off a wall wart and still be able to dim them. Nb - the dimming attachment is a small rheostat.

Your power draw is probably low enough for wall warts + rheostat dimmer.

Or you might consider
http://totaltransformers.com/dc-output-magnetic-20w-24v-led-driver.html

"BTW, I have searched for dimmable transformer, they are all in the range of $80-100 "

While they may call it a 'transformer" it is far more likely to be a small power supply.

Here is one that is less than $18.

Here is a link that might be useful: dimmable 'transfomer'

David and brickeyee, thank you for the info. I will check them out.

#1) I see the LED UCL DIY thread is full at 150 posts. Is there not a #2 thread? I wasn't able to find one :(

#2) I'm putting in a run of undercabinet lights - 32 watts under the cabinets, another 13.2 watts to light up two glass cabinets. The new mini dimmer switches that connect in series to the lights (i.e. the aluminum light bars from EV, Photonier, etc) that work with a non-dimming power supply seems like a very easy and inexpensive way to install, no? I do see they are rated for 40w per SuperBrightLEDs website.
-Does this suggest I should put my in-cabinet lights on a second power supply/circuit, in order to stay below 40w for the dimmer switch? I'm fine with all being on the same switch/dimmer.
-Can I just get a larger power supply (i.e. 100w from Photonier), split the power up into an undercabinet and in-cabinet run, and then use two mini dimmer switches? Guess I'm not sure if the 40w switch rating is for power in or power out/used....or both.

This has me reconsidering getting a dimming power supply instead, that will handle the entire run, and wiring in a wall switch......
To complicate things, I do have a second zone clear across the kitchen that will use one undercabinet 24" bar, and one in-cabinet 24" bar. This are definitely wants to use a single mini dimmer switch for both lights on a cheap power supply (i.e. reminds me of my laptop power cord). It's not really practical to run low voltage from my other power supply - well, I guess I could, but this area wants to be switched separately anyways.

You probably would be better off using a dimming power supply. The mini dimmer switches are rheostatic dimmers - the unused power is dissipated as heat.

If you want all the lights to dim together, a dimming power supply is needed.

If you choose thar route, you need to figure out the wire sizing(gauge) to each run as well.