but that won't give me the load reading of the psu. I have seen people who did load reading on the psu, and wonder how they did these tests.
You can get power supply testers from most pc places. They have a connecter that goes between the connector on the psu and the mobo/hdd/cdrom/whatever to test things under load. I'm sure you can imagine how to make a pass-through connector thing on your own. Be careful!