well... the psu is smaller than i would have suggested (i'd have probably used a 650) but it "should" be enough.
i cant imagine that one single fan is pushing you over your voltages since if it was your whole system would likely crash or have some pretty major issues and you would have noted that.
i find it odd though that you said the fan was working when things were unplugged. what did you mean unplugged from the back of the pc only? you mean like your monitor, speakers, mouse, keyboard? please specify.
also do you happen to have any sata to fan adapters or otherwise another adapter so you can try something other than a molex?
i'm hesitant to say you're over voltage but it could very well be a psu fault.
I'm sorry for the confusion. I meant that my keyboard, mouse, monitor, and turtle beaches were unplugged from the back of my computer, so you were right in your assumption.
I'm afraid I don't have any SATA to Molex adapters, but I am using the 3 pin fan to Molex connector provided by Cooler Master.
I also found it strange that only the fan doesn't work when everything else is on. I know that it would've crashed as well, which is why I am completely lost as to why this is happening. And I was actually thinking of upgrading to a more powerful PSU, like the Seasonic 650W 80 PLUS Gold, but I don't know if I can come up with money.