Hi,
A much better source of info about power supplies is one of my other haunts: Silent PC Review.
silentpcreview.com | Everything about Silent / Quiet Computers
Typical older units were in the 65-75% efficiency range (though some are lower), and now 80-85% are fairly common. A few units are approaching 90% now; and it also depends a lot on your actual consumption. Most computers are 100-200 watts of DC consumption, so add ~25-30% to that for the AC use.