that's a different issue.

the iphone 2g, like all ipods before it, could charge over firewire. since firewire can source a lot more current than usb, many companies made chargers that used the firewire pins in the dock connector so that it would charge faster.

the iphone 3g removed firewire completely (syncing over firewire was gone with the 5th gen ipod a few years earlier but charging remained), and any device that supplied power on those pins would cause that message to appear. the iphone 3g and later must charge via usb.

there are adapters that provide power on the usb pins from a charger that supplied it on the firewire pins, but i don't remember who makes them and a quick google search found one that has been discontinued.