Like all the higher current filters, the AF120 is a notch filter. I don't have one myself, and have never measured its response, but it should significantly attenuate noise in the X10 band. It should also reduce signal attenuation caused by a device plugged into the filter.
How well it works depends on how closely it is tuned to the noise or X10 signal. Unlike a low-pass filter like the XPPF, even slight mistuning of a high-Q notch filter will reduce its effectiveness. And, since it is a T-network with the leg of the T being a shunt capacitor to ground, it may also attenuate the X10 signal unless the input “arm” is tuned exactly to the X10 signal frequency.
All the computer power supplies I have taken apart have had capacitors directly across their AC power input to meet the FCC regulation on conducted radiation. So, they are not noise sources, but are serious signal suckers. Of course, my computer cases are almost a decade old, and manufacturers may be doing something entirely different now.
So, where does that leave you… It depends on whether your computer is a noise source or signal sucker. If it is a noise source, then adding a second AF120 in series should help. If it is a signal sucker, then possible attenuation from a slightly mistuned AF120 may be an issue, and adding a second AF120 in series may not help. Since you have a “hot” computer, you may be over the safe current rating of the XPPF filter. If not, that may be more effective than the AF120. The other option is to boost your X10 signal levels so attenuation from the computer doesn't matter.
Jeff
