Well for this one I simply used an extra power supply that was collecting dust. I like to run it constantly since the risk of mold is greater in a cooler. It's one of those power adapters that lets you switch voltages, and I keep it on the 2nd lowest setting...just enough to move the air a bit. I ran the wire for the fan and the wire for the oasis through a small hole I drilled in the back of the cooler which was then sealed with aquarium grade silicone.
I've also toyed around with splicing into the oasis line, but it reduced the airflow in the oasis' fan, plus I wanted it to run constantly (which is why I opted for a CPU fan as it barely gives off any heat), and I wanted to regulate the fan's output.
I wasn't going for anything fancy like I did with my frigador, just make use of what was available.