A +1 to Kill-a-watt or other at wall meter. Absolutely vital for any serious miner and cheap too.
If you want to get load on an individual card you need a clamp meter.
Clamp the power cables and record load when card is mining however remember the card gets "some" power through PCIe slot (20W to 75W depending on card - less on cars w/ dedicated power connectors). To measure that power load you need to use an extender and run the load extender cable through the clamp.