In my view right now I can see almost a dozen smartphone, tablet, and laptop chargers. Oh, and I can see another powering my Amazon Echo. And another charging up a pair of earbuds.

So yes, quite a few.

They're all plugged in, and most of them don't have devices attached to them.

This begs a few questions. How much power are they using? Should I unplug them? Are they safe?

See also: Top 10 iPhone accessories for 2018[1]

Rather than guess, I decided to break out my test gear and do some testing. My test meter of choice for this test is the WattsUp? PRO[2] power meter, as I can use this to measure how much power a device is drawing. While the WattsUp? PRO is a dedicated test meter, you can pick up domestic power meters from most online and brick-and-mortar electrical retailers these days.

Note: Power is priced in kilowatt hours[3] (KW h, or 1,000W), which is 3.6 million joules of energy. A device rated at 1,000W running for one hour will use 1KW h, while a device rated at 100W will take 10 hours to consume 1KW h.

As for costs, according to data published by the US Energy Information Administration[4] for September 2018, the average cost for 1KW h of electricity in the US hovered around $0.13. The most expensive residential power in the US is found in Hawaii, where it costs $0.32 per 1KW h.

I then took a genuine Apple iPhone charger and let it draw power (with nothing attached to it) over the course of a few days.

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