Reading the inflight magazine of the overcramped and underfed United Airlines last month, I noticed an ad from Kingston (I think) for a universal charger, costing around US$130. Universal chargers consist of an adjustable-voltage battery charger with a multitude of tips.
Problem is, universal chargers aren't. For example, no universal charger is going to include the unique data/power connector found on my Sony Clie PDA. Just ain't gonna happen. They should be renamed "semi-universal chargers."
There is, however, a new standard in universal charging emerging around the USB connector, which outputs 5 volts. Many new devices can be charged from your notebook computer's USB ports. In my collection of gadgets, for example, my Zen Micro MP3 player and a wireless mouse can recharge their batteries through USB. It can also work for cell phones and PDAs, if they are designed correctly.
(Tip for Zen Micro owners: it is better to recharge your unit through USB than via the wall charger.)
Another advantage of USB recharging is that you don't need to worry about outlets in international locations -- you need neither the right adapter for the wall outlet, nor the correct voltage and Hz converter. Also, you don't need to take along the power supply for each device; just a couple of short USB cables. I have a six-inch cable that fits the bill. Plus, you save $130.
The drawback: you need to carry your notebook computer with you. Or at least have access to someone else's computer. I recall an editor friend from England skulking aroound computers in the press room, looking for a free USB port to recharge his cell phone.