well dude, you putting 115VAC into a 12VDC fan
a wall outlet is not 12VDC
thats why you need a 12VDC power adapter.
you're lucky you did not hurt your self or burn down your house. consider your self extremely lucky!
i will take pictures of a simple 12VDC adapter i have wired up to run 12v PC fans and lights when i get home.