From what dave w said "YES the URL MECI filter I referenced, stops X10 in its tracks. You need to place the filter AT the noise source with any X10 control between the line and the filter.". I don't anticipate have a problem. I am planning to use these for a couple of TV's and stereo that doesn't have any kind of X10 control. So, I imagine plugging them in and then plugging the TV's & stereo into them would be OK.
Am I wrong ? If I am, please let me know so that I can avoid any problems.
I am not saying that it will cause any problems, it just won't do much for you. There are two types of noise filters, noise traps and noise blocks and as I said earlier, the MECI filter is probably a noise trap. A noise trap filters the noise by attracting the noise (including X10 signals) to it on either side of the filter and sucking the noise up . A noise block however will keep the noise on one side of the filter and the X10 signal on the other side of the filter.
If your problem is powerline noise and you have a very strong X10 signal, a noise trap will help you out, but if your problem is signal strength, a noise trap will actually weaken your X10 signal. It is because your UPS has a noise trap that you want to plug it into a noise block as it will prevent the X10 signal from getting to (and thus being absorbed by) the noise trap inside the UPS.
I hope this clarifies things a bit.