I bought a new notebook charging cable but there's always a green light, how much electricity does it use each month?

You can't switch off the green light, you have to pull the cable out of the power plug. Just seems to be a green led light.

No longer consumes like the power supply you had before. The green standby lamp hardly matters… Maybe 5 cents a month

And what if it is used up and goes out, does it harm the electricity connection?

What is consumed? I don't understand your question right now?

Why don't you just take a multiple socket with switch?

So you are sure that the monitor etc. Does not draw any electricity.

Your notebook consumes around 4 euro a year if you charge it every 2 days

The light goes out? After all, it's on for 24 hours.