There were not "power surges" in the older iPods. The issue is the inherent characteristics of Firewire vs. USB power sources. Firewire power specifications allow any supply voltage from about 12 to 48 volts to be delivered to the powered device & require the device to contain all the circuitry that converts it to steady voltages suitable for its power needs. USB power specs allow only a very tightly regulated 5 volts to be delivered to the device. Firewire sources are allowed to supply substantial amounts of power to devices before self-limiting; USB sources must shut down if more than one half ampere would be supplied to any device.
This is as non-technical as I can make it, but the bottom line is that these differences make Firewire power much less suitable than USB power for tiny devices like iPods that need only small amounts of low voltage power & add substantially to their bulk, cost, & complexity. By removing support for Firewire power, Apple can make smaller iPods with more features like accelerometers & more memory without increasing their price. This is a "win" for both engineering & marketing reasons: users that don't need support for Firewire charging aren't penalized with excess bulk or less bang for the buck & those that do need it can buy a converter like the Scosche or Griffin products.
However, this has nothing to do with error messages, inability to control the iPod, etc. Only a few car stereos exhibit this problem, mostly a few models made by Sony & Pioneer. It occurs because the companies are using their own protocols for the interface, not the ones Apple supports, either because they reverse engineered the dock interface without input from Apple or because they are trying to implement proprietary features in ways the iPod wasn't designed to support.
There can be no universal adapter for this because the solutions vary according to how the maker has implemented the interface. It could be that they have tried to emulate the iTunes interface, either using the Firewire or USB signal (not power) pins, to read data from the iPod. It could be that they are using the Apple Accessory Protocol pins for control or data communication but haven't implemented the protocols correctly, for instance by not keeping the timing within Apple specifications. It could be a combination of these & other things -- there are at least eight digital signal pins in the dock connector plus their respective grounds, so their are a lot of ways to get it wrong, especially if you try to push a lot of data through the connector quickly.
Again, I'm trying to keep this as non-technical as I can but basically there are three types of interface connections in the dock connector: power, analog audio, & digital data. Power issues are straightforward -- if the accessory supplies Firewire power on the Firewire power pins it won't charge the new iPods but a simple converter fixes that. There shouldn't be any problems with the analog audio connections -- they supply the same, standard line level signals as any other analog audio device. But any issues with the digital interface are extremely unlikely to be correctable with a simple adapter that can be inserted between the accessory & the iPod. Most issues will take substantial computing power to correct & if it can't be accomplished in a modification of the accessory (like a firmware upgrade, if that is possible) then there is little hope that accessory will ever be able to work with the newer iPods.
