How to measure your PC's power usage

I use several smart plugs around my home to control devices remotely from my phone. They can also display live voltage, current and power consumption, along with graphical displays of past kw/h.
The numbers look accurate to me and at €5 each great value.
 
I don't see why. I run my PC on unlocked ultimate power setting, high performance cooling mode and over clocked gpu. I really don't want to know haha