Any DC power pack is designed to safely offer a certain measured maximum number of volts, and also the commensurate amperage, to drive toy locomotives. All the lights and motors therein require a piece of the finite pie coming down the output wires from the power pack.
One engine hauling a bunch of cars, struggling up a 2% grade, and in good running order, may take 12 volts or more, and about 0.8 amp. If you also have lots of street lighting and some signals operating from the same power pack, your system may be taxed, and may overheat. But it would be a worn or inferior product if all it could do was that.
A better (read "more powerful") pack would permit some street lighting, signals, and two or three hard-working engines. An even more powerful one would offer even more current to run more engines. But I understand that this is not the nature of your interest.
It is no different in DCC. The power supply plugged into a wall circuit can only throughput so much current. Every electronic item will insist on its designed share of that same finite pie. Even DCC systems overheat and will shut down if you ask them to do too much.
What I am saying is that if your current system meets and exceeds your needs, is there any other reason to want to part with some cash? If you have a hankering for "something else", maybe now is the time to seriously investigate all that DCC can offer you. If you like, we can cover some of that, but if you really are content with the way things work, including in DC, I would counsel against spending any money. When your circumstances change significantly, then would be the time to look at more power in whatever form makes sense.
If you are interested in some fancier operating capabilities with the engines, say smoother starting, and acceleration behaviours, I would tell you that DCC offers that and much more. On the other hand, a motor that behaves poorly in DC operations almost always runs as poorly, or even worse (!), in DCC.
-Crandell
