Hope you're not planning on those for any kind of plants and just ambient lighting as they're not plant capable really, just accent light.
As for power, an average LED draws 20ma, x 36 LED's x 3 stripes ~= [email protected]
, so a 12v power supply from an old cordless phone, electronic, etc, at around 2amps.
Now the problem is most "wallwart" power supplies are unregulated, meaning when they say [email protected]
, they put 12v at around 700ma. If you run it on something that only draws 200ma, it will run more than 12v and probably fry it. So by my above calculations, each strip will need about [email protected]
if you intended to wire them to different tanks or different power sources.
using an old computer power supply, while big, is regulated and you can power LED's, fans, etc, all from it and have 12v power at whatever power you need.