Q: ??need to know as the electric bill would be high thanks in advance- regards,Greg (-":
A: It will probably not use all 640 watts all the time, unless you have a lot of energy intensive devices inside your computer like a high-end graphics card or neon lights, etc. The link below will let you calculate how much energy your computer is actually using to run your computer. Since the PSU only puts out as much as is required from it (plus a littel overhead), your energy bill will not suffer from having a larger PSU unless your computer actaully needs all of that wattage... http://educations.newegg.com/tool/psucalc/index.html