Charging Apple Watch series 4 with iMac question

[Benz63amg]

For convenience reasons, I’ve plugged in the Apple watch charging cable into the USB port in the back of my 2019 iMac so that I can charge my Apple Watch in an easier manner and I was wondering whether having that Apple Watch USB charging cable plugged in at all times in the iMac use up extra power (when NOT in use and NOT charging the Apple Watch) or put any strain on my iMac?

I used to always use the apple wall charger to charge my Apple Watch series 4 every other day when the battery got low but I got sick of plugging and unplugging the dedicated Apple charger into the wall outlet so I figured I’ll permanently connect just the Apple Watch charging USB cable directly into my iMac and charge the watch that way but is it now wasting electricity when connected to my iMac and When it isn’t actively charging my Apple Watch?

 

[Shirasaki]

The charging cable itself does not create a full electrical circuit to draw power from any power source. It needs a device it is designed to work with to create a circuit and deliver power from the source.

 

[johannnn]

It doesn't put any strain at all on your iMac. You're not wasting electricity at all.

 

[Benz63amg]

The charging cable itself does not create a full electrical circuit to draw power from any power source. It needs a device it is designed to work with to create a circuit and deliver power from the source.

Thank you
[automerge]1596596360[/automerge]

It doesn't put any strain at all on your iMac. You're not wasting electricity at all.

Thank you, Much appreciated. I have another question regarding which wall charger I should keep plugged into the Wall outlet at all times for charging my iPhone 11 Pro, Is the 18W Charger that came with my iPhone 11 Pro more efficient in power usage compared to my 12W iPad Charger from several years back or would the 18W iPhone 11 Pro charger use up more electricity at all times due to it being an 18W charger and the iPad Charger being 12W?