John,
The 10A power supply is wires into the NEC booster; the NEC command station also plugs into the booster; the output from the booster is then wired to the track. This isn’t regular DC; the DCC is power with the command signals overlaid on it.
On larger layouts, say, 100+ feet of track, you can split your wires to the track and tie them in at one or more different places (like at opposite ends of a loop, or far ends of a point-to-point). This multi-point tie-in can help overcome irregularities in joiner conductivity.
Here’s some further info from Greg, who’s been into these details for many moons:
https://elmassian.com/index.php/dcc/dcc-wiring-tips
https://elmassian.com/index.php/dcc/my-implement
However, are you talking about running DC and DCC on the same layout? I don’t think you can do that simultaneously; as far as I know (and someone please correct me if I’m not) it has to be one or the other, DC or DCC (perhaps via swapping connectors at the feed to the track).