Calculating AC Input Power
The product of Irms and Vrms is not real power. 

Imagine if the load was a perfect capacitor and input was a pure sine wave. 

RMS voltage is mains voltage. RMS current is Vrms/Xc where Xc = \$\frac{1}{2 \pi f C}\$

Say 120VAC RMS and 100\$\mu\$F, so Xc is 1592\$\Omega\$ and Irms is 75.4mA, so we get 9W. 

However real power is exactly zero. 

To get input power you need to find the average of the instantaneous product of voltage and current. In other words, a wattmeter.