One thing you can do is run several devices off of one power supply,
> if you have enough of them with the same voltage demands.
You have to be very careful when attempting this with devices that have external connections to other systems. Some wall-wart-powered gadgets rely on the isolation provided by the power supply to implement various regulation and voltage-splitting tricks. That is, the negative side of the power input may not be at the same level as common of any i/o port. If you try to power two devices that disagree about common from the same supply and they share some other common path you will at best cause failure and possibly cause damage.
I have an IR i/o box whose power-input, IR-in/out, and RS232 commons are all different. Of course, this kind of problem can bite you even without sharing power supplies. I have a text-to-speech box whose audio-out "ground" is really the bottom leg of a push-pull driver of some sort. If I plugged this output into a grounded amplifier without an isolation transformer the driver would be shorted through my computer's ground connection to the box's RS232 port.
Dan Lanciani ddl@danlan.*com