"The Natural Philosopher" wrote in message
news
trouble wih almost all 'power meters' is that they dont measure RMS power,
they tend to measure VA or some approximation to RMS that falls down badly
when faced with a switched mode power supply

Unless you know how they are measuring the power, be careful.

The one I have (somewhere!) can be switched between power in W and power in
VA, and gives the same result for a lightbulb (being resistive) but
different results for anything with a switched mode power supply. That was a
bog-standard meter from Maplin (RIP). It also had a setting that calculated
total energy used (ie power integrated over time) in kWhr.