PDO's PowerTwo includes two separate charging devices: a 12-volt charger that you can use in a car, and a wall adapter. The version I tested is compatible only with the iPod classic, iPod nano, and previous versions of those two iPods. According to a PDO representative, the PowerTwo isn't compatible with the iPod touch and iPhone because those two devices have different power requirements. (PDO clearly lists its compatibility list on the PDO Web site.) PDO says that an updated version that's compatible with all iPods and the iPhone will be released in "one to two month's time."
The 12-volt charger has a permanently-attached coiled cable. The cable has a 3.5mm audio-out jack so you can plug in a cassette adapter or auxiliary cable to your car stereo, or you can even connect headphones and listen to your iPod. The audio through this jack sounded just like the audio from the iPod's headphone jack, but it's not as loud. When the iPod is at full volume, audio through the 12-volt adapter's jack sounds at about 80 percent when compared to the volume coming from the iPod's headphone jack.
The 12-volt charger has a LED to tell you that the adapter is receiving power, but it doesn't indicate when the iPod is fully charged. I was able to easily plug the 12-volt adapter into the recessed 12-volt socket of my 1994 Ford Explorer.
The wall adapter looks a lot like Sonnet's USB Wall Charger for iPod ($20). It's small enough (1.50-by-2.00-by-1.25 inches) to fit in a pocket, but it will block any outlets below it in a vertical arrangement on a power strip or wall outlet (if you flip it upside down and plug it into the top wall outlet, the bottom outlet is unobstructed).
The wall adapter includes a removable USB dock-connector cable that can be used to sync your iPod with your Mac. Like the 12-volt adapter, there's an LED to tell you that the adapter is getting power, but it's not an indicator LED to tell you when your iPod is charged. You can fold in the prongs when you're not using the wall adapter.
The 2-in-1's adapters don't offer any special features, but they do the job, and they come at an attractive price--you get two adapters for the price of a single Apple iPod USB Power Adapter. You can leave the 12-volt charger in your car, and the wall adapter is small enough to carry with you.