Whenever I turn off my cheap airfreshner it also cuts my monitor out too! https://photos.app.goo.gl/gmbHYUS7a9cUYkwg1
its definitely something to do with the way you have your plugs wired up nothing to do with the computer
I think it's because they are on the same extension lead. So when I turn off the airfreshner there is a surge from somewhere and sensitive electronics cut out for a bit. Using vintage fans also messed around with my old monitors USB transformer for the internal hub. So Everytime I turned it off the hub would cut off and I'd hear the windows disconnect noise
Sounds like some of your devices don't have or have faulty snubber devices on the AC input and I know for a fact that your vintage fans wont have snubbers on their power switches. Snubbers are basically a small capacitor and a resistor in series that suppress arcing in switches and helps prevent devices from causing voltage spikes which can cause what you're describing with your monitors.
Did it again and it cut the mouse off which was surprising, the mouse is powered exclusively from USB, so this voltage spike is going straight through my motherboard *shocked face*
It's not always a spike, a component without a snubber can also emit EMI on the AC line (this is what effects digital components the most) which I've sometimes heard thru amplifiers as a *pop* from light switches, older components that don't have subbers and sometimes gear with a high inrush current due to having large AC filtering capacitors, some larger pro amps have been known to blow RCDs when power on after a sitting for a while.
If you use a power strip to power your monitor, computer and the airfreshner, check the maximum Wattage of the power strip. I doubt it's that but many strips have a low limit...
Read above, its nothing to do with a limit of current. The power strip is rated for around 3KW and I'm not pulling that through. Yes an OC'ed i5 4690k can draw a lot of power but not that much.