The reason I ask is the DCS signal is susceptible to line noise from the power source. If there's a lot of noise on the 120V side, that passes through the train transformer and TIU/WTIU and gets superimposed on the DCS signal. That can confuse the trains trying to decode the DCS signal. Case in point, there have been recent discussions here on the forum about how the WTIU seems to have problems when powered by transformers with less than a pure sine wave output.
A suitable Line Power Conditioned filters out the noise and passes a much cleaner 60Hz 120V sine wave onto whatever's plugged into it's output. In this case your layout.
