So I own a rather expensive PC monitor, an Acer Predator 34" 21:9 curved 3440x1440.
Here's the weird thing. When I plug something into the USB port, frequently the monitor switches it's display off for a few seconds and back on. Rather alarming you might agree.
Today when I fired up my new DSO (Owon1022i) it did it when I connected the ground probe to the 0V rail of my bread board.
Now here's the twist. The DSO was not connected to that PC. It was connected a laptop completely separately. A diagram might be a bit hard to do here, but I'll have a go.
Mains <---> Monitor
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Mains <---> PC <---> HDMI <--> Monitor
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Mains <---> Laptop <---> DSO <---> Bread board PSU 0V rail.
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Mains <---> Wall wart <-9V-> Bread board PSU (0-5V)
That's quite a long way and quite a lot of power supplies for any glitch to get through.
The DSO did capture a small spike, but I didn't drill into it to work out what voltage or period it was. Bizarrely the actual probe was not connected, it was sitting on the desk, so what exactly did the DSO capture!?