Is all this easier than getting a DC adapter?
Okay, I'm the one who told Ben Heckendorn (VCSp) about the power requirements of the 2600. Here's the deal:
The power input of the 2600 is fed directly into a 7805 regulator. This regulator can take an input voltage of up to about 30V and limits it to 5V for the TTL-MOS IC's. It has a dropout voltage of 2V, which means the input must be at least 7V for it to operate. This means, theoretically, the 2600 could run on 7-30V DC.
The 2600 also provides about 7.5V to the color adjustment circuit, and it has crude voltage regulation here as well. If your input voltage drops too close the 7V, the color will stop working, then if it drops below 7V, your 5V to the IC's will drop.
The upshot of all this, is that you should be able to run a 2600 from 8-12V or higher with no problems. Atari's own schematics for the 2600 specify 14VDC at the power input. For safety's sake, I wouldn't go any higher than that, however.
-Bry