Adding camera to power supply box

This is a curiosity killed the cat kind of question, and kind of a stupid newbie question.

Electricity makes me nervous so I always play it safe and unplug the power supply box before adding a new camera to the supply. But is it necessary to turn off the power before using a screw driver to tighten/loosen the screws or is it just a matter of making sure to not touch both the positive and negative screws at the same time?

I'd like to not get electrocuted, so I figured it be best to ask before I decided to be stupid and feel the zap from a 24VAC power supply.

I ask that question to ask this next one. Even if it is hypothetically safe to leave the power on, what to do you do when you need to add a camera? Leave it on, or turn it off?

Thanks in advance for any tips and advice.

Your not going to feel a zap from 24Vac however the best policy is to turn the power off simply to protect everything in the event of you doing something silly. I've been doing this stuff for 45 years and still do the occassional silly thing.

The other thing is that some power supplies have a soft power up and dont like a sudden change in load which would happen if the power is left on and other devices are connected especially if they draw a bit of current