Some monitors actually are powered from external adapter. No idea how common it is, but one is sitting on my desk.

Interestingly, it's also the one that turns off when there's some interference from the lights turning off in the next room,...

I guess I'll try re-arranging the wires if that stops the pickup of interference.

> Some monitors actually are powered from external adapter. No idea how common it is, but one is sitting on my desk.

I vaguely remember it was for regulatory reasons. I searched around and it looks like it's because with an external power supply they only need to certify the brick rather than the whole unit https://www.reddit.com/r/sysadmin/comments/24jxfj/anyone_els...

It being thinner is also a bonus.

>Some monitors actually are powered from external adapter. No idea how common it is, but one is sitting on my desk.

Well that's just AC/DC which is similar to the PSU of a computer or laptop. The monitor, itself, has voltage regulation for much lower volts that the one connected to the mains.

> Interestingly, it's also the one that turns off when there's some interference from the lights turning off in the next room,...

My Samsung monitor (actually a TV) does this, with any spike/dip on the mains line (eg the fridge turning on). I assumed this was just poor quality power circuitry.

Is yours a Samsung too by chance?

Both my monitors have an external brick. Unless that is something else?

This is exactly the same as the laptops have a power brick, or desktops have a PSU. It's relatively dumb AC/DC switch mode power supply (say ~90-230 to 18VDC) w/o any major care about ripple (100mV ripple is amazing already) or even exact voltage. The monitors do have more voltage regulation inside.

Yes, that reason is easier UL and CE certification.