And, like what will happen if I throw in crysis with my current psu?
What do you mean ? Are you asking if Crysis could cause your computer to require so much power that a 380w psu might pop ? If yes, the answer is no, your computer will run Crysis as well as it can, and you won't come anywhere near blowing the psu up in the process.
ok thats great , my last question is, Would I be able to run my computer on the 250w for a bit, it would be for a few days or so?
You could try it, don't think I'd try playing Crysis with it though.