Power bricks should be fine. I'd suggest starting out with a pretty low voltage (5, maybe up to 9), in DC.
Keep in mind though, that while these voltages are generally below the threshold required to conduct through skin, and represent little shock hazard, pretty much any electrical system can be hazardous in other ways.
In particular, you can create a fire hazard even with pretty low voltages, if the resistance is low enough and your power supply is capable of providing enough current. Likewise for sparks: if, FSM forbid, you happen to have some explosive vapors around (and even a bottle of fingernail polish remover can be a source of explosive vapors), a small spark can start a fire.
My point isn't to try to scare you off, but rather to say that you always need to be cautious, pay attention to what you're doing, and keep safety in mind, even when playing with low voltages.
Keep in mind though, that while these voltages are generally below the threshold required to conduct through skin, and represent little shock hazard, pretty much any electrical system can be hazardous in other ways.
In particular, you can create a fire hazard even with pretty low voltages, if the resistance is low enough and your power supply is capable of providing enough current. Likewise for sparks: if, FSM forbid, you happen to have some explosive vapors around (and even a bottle of fingernail polish remover can be a source of explosive vapors), a small spark can start a fire.
My point isn't to try to scare you off, but rather to say that you always need to be cautious, pay attention to what you're doing, and keep safety in mind, even when playing with low voltages.