Here is the history:

When DCC first came out, part of the spec was for the programming track (service mode). Since it was expected that locomotives would need to have decoders added and there was a high probability of wiring errors, the spec limits the current on the program track to 250mA to prevent decoder damage in the instance of a wiring error. Most command stations met this requirement by simply using a series resistor to limit the current. This worked quite well until sound decoders came out. Sound decoders generally have quite large input capacitors to store energy so that the sound will not be affected by short power losses to dirt, frogs, etc. The problem was that the sound decoders could not draw enough current through the series resistor to charge the input capacitor in time to meet the programming requirements. Enter the Power Pax. The Power Pax uses a circuit breaker to limit the current to less than 250mA, but allows up to 250 mA to quickly charge the input capacitors on sound decoders. The Power Pax does not provide any programming signal, it simply repeats the programming signal produced by the programming track, but at a higher available current than the standard programming track. As you may know, that has worked well for quite nearly 20 years.

Now that DCC is included with the locomotive, or at least an option to simply plug in a second party decoder, the concern over damaging am incorrectly wired decoder is almost moot, but the most recent sound decoders clearly need more current. This resulted in decoder manufacturers producing their own programming devices. Since these programmers were no longer compliant to the service mode standard (current not limited), the manufacturers apparently felt they could take other liberties with the programming methodology. Either by accident or on purpose, changes were made so that the decoder would not work with the programming timing of the Power Pax/Program Track combination (which is NMRA compliant). You will note Paragon2 and Paragon3 decoders from BLI (for example) encourages you to use Program on Main (or Operations Mode) to program CVs and gives you a verbal feedback of the CV value. They have basically circumvented the need for the Program Track. SoundTraxx makes their own PTB-100 and the Tsunami2 no longer requires a Program Track Booster of any type. ESU Loksound makes their LokProgrammer and the ESU V5 decoders no longer require a dedicated Program Track Booster either.

So the bottom line is the Power Pax may work with whatever you have so far, but the newer more complex sound decoders may need their own programmer [or none at all]. That's why we recommend the NCE Power Cab. You can use it as a normal throttle on the layout, but also use it for service mode to program and read back CV values. To the best of our knowledge, the Power Cab has modified its timing so that it will work with the various new decoders that won't work with the original service mode, and of course it has 1.5 amp capability to charge and power up any sound decoder.