Is it possible to measure the load on my PSU?

I am wanting to add some components to my rig, but I'm not sure that the PSU is big enough. I know there are various PSU calculators online but each of them gives me a different number - one tells me that I need 600W while another tells me that I need 1100W.

Also I know the method of looking at the specs of the components and adding up the total load they they will put on the various rails, but I was wondering if there is any way to actually measure the load that is being put on the PSU? Is there some utility or something that can somehow measure how much power each component is using?

Or "something
Back when I upgraded my first Core2 system, I spent 30 minutes taking measurements with a clamp-on DC ammeter. On the main power connector, I bunched together all the wires of the same color and clamped the ammeter around them. Likewise for the CPU and GPU power plugs. Made individual readings and added them together.

Power consumption of the complete system can be measured with a Kill-A-Watt meter. Multiply that by the efficiency of the PSU at that power level and you'll come very close to actual total power consumption of all of your components.

I know of no programs that will do this.