Depends on the charger but either effectively zero or considerably less.
People get pissy about it, but think of electricity like water. Having a longer pipe is a negligible amount of water if the faucet is still off. And the faucet can only turn on if your device completes the circuit by being plugged in (and doing the appropriate handshakes)
That said, some chargers will consume a negligible amount of electricity to actively listen for a device. Think of it like the water in your toilet. Every so often enough evaporates or leaks that you hear it run a bit to refill. But mostly it is nothing until you flush.
I use a short lightning cable to plug my phone to my car for carplay. I just leave it plugged into the usb port (without the phone) when I’m not in the car. Do you think it’s slowly draining some energy from the car battery?
The cables themselves do not use power. It is the brick.
Your radio being off would not push any power through a cable. Also your cigarette lighter being off would not push any power. Which is why plugging it in won’t do anything.
To continue the metaphor - your water is turned off. You can’t use up water that isn’t there.
The reason the brick uses power is because it is available 24/7 for you to plug something in - and when you do - it can ask that device how much power it wants - does it have fast charging? Etcetera.
Thanks. About the cigarette lighter - my dashcam plugs into it but I always unplug it before I turn the car off so never noticed if the camera turns off along with the car. If it does, does that mean I can just keep the dashcam plugged in and it won’t draw power even though the camera is connected on the other end? Or does closing the circuit mean it will start drawing power?
The water analogy is perfectly fine for many situations, but the reason these don’t draw a lot of power when nothing is plugged in isn’t because a “valve is off”. There’s a transformer, so this is like two separate water lines. If the charger is plugged in, there’s always a closed circuit on the mains side of the transformer, even if there’s an open circuit on the DC side. See the first diagram here: circuitdigest.com/…/ac-to-dc-converter-circuit-di….
The reason new chargers don’t use as much power with no device attached is because of better design. If you checked an old charger or some crappy power supply, they’ll use a fair bit of power even with nothing on the DC side. It’s not enough that one would matter, but it is enough that there was an industry wide initiative to reduce phantom load resulting in new chargers that use almost nothing when nothing is on the DC.