Putting this in the notebooks section because A) the notebooks are Dell, the monitors are not; and B) we didn't have this problem until we got our newer notebooks.
The problem is that with a notebook plugged in to the same power outlet as an external flat-panel monitor, the external monitor has a subtle flicker.
Flicker description: SUBTLE. Annoying as hell to work with, but it's not like the image is flickering on and off. It looks like a PHASE problem.
First observed when I bought my then-new XPS M1530 (which I adore) along with a 22-inch Dell flat-panel. Went back and forth with Dell support, replaced that monitor with a new Dell, same problem... gave up, went and bought something else (Westinghouse), same problem, and finally thought about the fact that it looked like power phase. Tried several options until I found that if I ran an extension across the room to a different outlet, so that I could plug my monitor in behind my desk but my XPS across the room (same circuit, I think), the flicker went away.
Note that when I unplug my XPS and run it on battery, a tiny bit of visual disturbance is visible on the external monitor, even though they're now not plugged in to the same power outlet. So there's still something about driving visual from the XPS to the external monitor.
At the same time as the above, my partner had HIS notebook (older Inspiron) and a flat-panel external monitor running in the same small room, maybe 8 feet away from me. Both were plugged in to the same power strip. No flicker at all --everything's gorgeous. But a few days ago I got him a new machine: Studio 15 (pretty nice, though not as nice as the XPS). Sure enough, now he has the same subtle flicker on his external monitor unless he separates the power source.
But now we have a new problem:
We're now talking 4 devices: Two notebooks, two external monitors. We have three power outlet sites in the room. We've tried every combination, but the 4 things won't play nice together. We have to have each on its own outlet. The ONLY way we can run all four without any flicker on one of the monitors is to run an extension out of the room.
It's weird that it doesn't appear to be a circuit thing. Just the outlet sites. And it's weird that Dell support didn't seem to know there's this problem (though I admit I have not tried to hook these up in some other house somewhere!, so maybe we just have a ghost or something stupid).
I don't want to have extension cords running all over the house just so we can run our office. But without knowing exactly what the problem is, I'm stumped for a solution.
Looks like the Studio 15 video card is Intel Graphics Media Accelerator 4500 MHD. On the XPS, it looks like... NVIDIA GeForce 8600MGT. Both, obviously, are 64-bit.
Anybody have a clue?
SOLVED... or so it appears. I thought of just removing my post, but I guess I should leave it up in case it helps someone else.
Here is the surprising deal: It seems to be an issue of a ground-loop.
Evidence: Previous Inspiron notebook with which both of the external monitors worked fine had only a two-prong power supply.
The theory is that with the three-prong power supply (now standard, especially with the apparently shock-inducing XPS notebook), the notebook is grounded... and the external monitor is grounded through the VGA connection to the notebook but also at the same time via its own ground plug. My understanding is that modern equipment should NOT have a problem with this... but then again, there's this flicker we've been seeing!
Introduced a slightly modified two-prong power cord between one of the external monitors and the power outlet. Then plugged the corresponding notebook into the same power outlet. NO FLICKER.
Have not yet tried the other pair (other notebook and other monitor), but expect the same rock-solid results (just had to actually WORK today, LOL!).
Which part of this setup should be addressed by the responsible manufacturer? I'm thinking Dell, due to the power supplies... In any case, if you have subtle flicker, this is something to try. Of course, bear in mind that your external monitor will now NOT be grounded whenever you disconnect the notebook, so you need to devise your own safety procedure, i.e. unplug the monitor from power whenever you disconnect it from your notebook. These days the risk of a shock or damage is low, I think, but there's no sense in being sloppy!
Let us know, please!
And do remember that now your monitor will be more vulnerable if/when it's NOT connected to the laptop. We're currently using a modified 2-prong power cord (the modification being carving away the plastic a bit so that the grounding pin has somewhere to go when the two prongs are inserted... I should take a photo, I guess!), but ultimately some kind of easy disconnect would be better --so if you are unplugging the notebook, it's easy to at the same time unplug the monitor, meaning it stays safe.
I'm in Florida. We get a LOT of electrical storms. I just don't want my monitor frying when it's not even in use because I've got my laptop in the kitchen...
Anyway, let me know if it works!