mitch04 said:hmm so there would be no chance for my power supply to run it? I might just buy one on ebay for like $40 for a 500 watts
fullmetalvegan said:You'd really be pushing it on 400W, I wouldn't risk it. Note also, PSU's lose power efficiency over a yearly basis, so it may only put out 350W or 300W if you'd have it for a year or more, for example.
It's safe and more reliable to purchase a new 550W to give your PSU the extra power it needs to run the system and be able to breathe. On 400W it'd be running at max to put out the power which means it could overheat and die very quickly.