[grep]

your not looking for total system amperage. what you want is the total amperage at each voltage. ie. the total amperage at +3.3 volts, and the total amperage at +5 volts and the total amperage at +12 volts now you can convert each to watts and compare the results with your power supply specs. This makes it possible to find out if that water pump is ok on your system or if that bunch of fans is too much or not. Most powersupplies may be rated at 300 watts but the 3.3 + 5 volts are rated combined at a fraction of that total.
example might be
350 watts total
175 watts on 3.3 volts
150 watts on +5 volts
but when the 3.3 and the 5 are added together they can not exceed 210 watts. Far less than the 175 + 150 the specs show for those voltages.
so how can you know how much your system is using on 3.3 volts
and how much its using on 5 volts.
by actually measuring it of course.
theres the problem, how?
what I am talking about is how with commonly available equipment.

Grep