Well
That depends on what KIND of PSU it is.... If it is some cheap thing that came with your case than it could be an issue. Basically you get what you pay for when it comes to a PSU. For example go into your local pc store and pic up a $30 psu and then pic up a $100 psu, your going to notice that the $100 PSU is twice as heavy. Along with that look at the power ratings, particularly the 12v output. Your going to notice that the more expensive PSU is going to put out a more efficient current.
If you think your PSU is decent and you cant afford a newer better one. Try it. Worse comes to worse it will burn out and you will have to get a new one anyway.
But I think 400 watts might be cutting it a little thin with the amount of devices you are running/going to be running. But I could be wrong so anyone feel free to correct me. Put it this way I have 7 case fans, 1 HS FAN that runs directly to the psu, 2-rom drives, 3 hard drives, video card that requires power and 2 cool cathode neon lights. And I have a decent 500 watt PSU wich does fine. Would I run a 400 ? Probably not. With numberous devices on your system that require power, the bigger the better in a PSU.
And as I said before you get what you pay for in a PSU but dont pay too much. If you see a 500 watt PSU selling for $125 look at one for 500 watt $65-100 and compair the power ratings. Most of the time you are paying a extreme amount due to a name. Antec, Enermax, Thermaltake. Anything within 475-500watt over $65 will do you fine.
