i'm afraid that there is no software

that can give u the real time power supply

.....
check these links they will estimate the power consumption of your pc thats it.....you can check the input by using an ammeter

and a voltmeter

......

....no software can estimate the power consumtion......until now....if any new one invents it i am happy!!!!!!!!
*www.journeysystems.com/?power_supply_calculator
there is a gadget named "kill a watt"....which also gives power consumption.....check this....*www.thinkgeek.com/gadgets/electronic/7657/?cpg=cj