Hi The current draw from n scale engines is really small. I run 6 diesels simultaneously (with NCE, TCS, Lenz/Atlas, ESU, DigiTrax, and ESU/Atlas decoders). I can have 6 to 8 engines idling around the layout, and the 6 running, with a total current draw of less than 900mA (I use the NCE PowerCab- 2Amps output). So, I would say the large decoders are not necessary. Do pay attention to how the decoder is covered (or not) with Kapton or similar tape- you need to allow the heat to get away from the chips.