Thanks to Alvin for selling me his CDC. After ripping it apart a few times.
Here's what I found out. The "internal" power supply is actually a TDK switching power supplies rated at 12V, 12.5Amp, 150W. If you need the actually electrical and mechanical specification, let me know.
The CDC has no problem handling my TX pack which consist of 8 x Sanyo NiMh. I can charge it with no problem, and I can discharge it as well.
Now, whether you would like an external power supply, it is up to you. For me, I like an integrated charger and I don't use lead acid battery. For Alvin, he prefer that, so I guess he sold it to me.
Also, Don't have too high of expectation from the internal power supply. when I tried to connect my Eagle pocket charger which charge at 4Amp to it, the CDC reported of too low of voltage to work correctly. I guess it is usable for powering so stuff, but not good enough for a second charger.
By the way, you should be able get Switching Power Supplies from your local electronics store. In Singapore, you should be able to get AC/DC switching power supplies rate at 16A. the last time I checked, it is SG$160.
I don't think the CDC charger can handle an input up to 24V. Anyway, if given more than 12V, the voltage regulator will kick in and bring it down to 12V.
The CDC come with a switching power supply. It doesn't have big heavy transformer. So, it is pretty light. Switching power supply work differently than a regular set-down transformer and regulator.
Hope that helps.