There is no software at the moment (there are plans in the works for a new ESA standard which would have sensors in the important components and then you can monitor them with software, but this hasn't taken hold yet). If you were worried about power use, about all you can use is a kill-a-watt but Cheetos used the wrong terminology:
Originally Posted by Cheetos316
Perhaps you should think about getting a power meter such as the Kill-A-Watt
to measure the wattage at the outlet. Only then will you know exactly how much your PSU is needing since software monitoring can never account for the inefficiency of the PSU.
Current software monitoring can only monitor voltages through sensors in the motherboard. The traces and connections before these sensors skew the voltage readings by adding resistance. Because of this, current software monitoring is inherently flawed. The kill-a-watt is a good recommendation, but it cannot account for efficiency of the PSU either. It will only read AC wattage, and the efficiency number for a PSU is what is lost when converting to DC which is what the computer in run on and what PSUs are rated by. mortimersnerd is correct that efficiency is usually on a curve, but you can usually go with an estimate based on known values for you PSU.
So, the only software available can measure voltages but not acurately. The important things you want to know about your PSU health (temp, voltage, power consumption) can only be measure physically with multi-meters, temperature probes and power consumption devices like a kill-a-watt.