i would go with the 550w since its cheaper (and has an LED light fan )
but lots of people say go with 700w cus its safer.
but then again, my build isnt very demanding:
Case: Coolermaster Storm Enforcer
CPU: AMD Phenom X4 II 955 Black Edition
CPU Cooler: Arctic Cooling Alpine 64 Pro Rev 2
Graphics Card: NVIDIA Gigabyte GTS 450 OC
HDD: Western Digital Caviar Blue 500GB WD5000AAKX
SSD: OCZ Agility 3 60GB SSD 2.5"
RAM: Corsair CMV4GX3M1A1333C9 4GB (1x4GB) DDR3 (im getting two of these)
Motherboard: ASUS M5A97 Motherboard
Optical Drive: ASUS DRW-24B3ST 24X DVDRW Drive
Power supply: Either one listed above, please help me choose!
Monitor: Samsung S22A300B 21.5in Widescreen LED Monitor
Mouse: Gigabyte Eco 600 Wireless Laser Mouse
Keyboard: Cherry Infinity USB Keyboard
OS: Windows 7 Home Premium 64 bit OEM
So what should I do with the power supply? do i really need 700W?
You can tell precisiely how much PSU power your system requires in both watts and 12v rail amps. from the link below which will also show you how to determine which PSUs are quality, reliable PSUs from objective, scientific testing and physical inspection of the internal components. No guessing or subjective opinions required. Be sure to read test reviews for the exact model of PSU you are interested in as all models in a series are not of the same quality.