Interesting bit of information I found today:
If a laptop I have is plugged into the wall and turned off, the adapter produces about 50-60mV of dirty electricity. If the laptop is on, it does not. So, it may be a good idea to unplug any switching adapters that have no draw on them.
Re: Dirty Electricity with no Draw on Power Adapter
I haven't measured what the voltage ripple is with the power off, but a lot of my AC adapters generate heat even when the device they power is off, or they have a light that stays on. I've always assumed that they emit line noise whenever they're plugged in, but it's interesting if yours is better the draw is low. I still need to get that oscilloscope :(
Most of the filters I've built are tuned to filter best when the draw is low because I didn't have big enough toroids, but I still unplug stuff on general principles.