I have a 250 watt PSU( Hewlett Packard OEM) and I am not sure how they are rated with these power supplies, it currently powers: 8 in 1 card reader, DVD+RW, CD-ROM, Floppy Drive, HDD, and has 1 more power source. Would i be able to add an FX 5900 to this kind of power supply?(currently powering a P4 2.8 Ghz HT)