This is also a good web site for reviewing PSU. They explain in very details of each part of a PSU
http://www.hardwaresecrets.com/article/936/7
"OCZ ModXStream Pro 600 W can really deliver its labeled power, however during test five it shut down twice."
Sometimes the overload protection circuit will shutdown a PSU if the loading exceeds its max power output. It depends on how sensitive the manufacturer makes it.