Is there a USB wall charger that "just works" with every device?
Sony PS3 AC adaptor
I have found it! The amazing PS3 adaptor does the job. It is a full USB host and will charge any USB standards compliant device under the sun!
Details
After spending weeks going through dozens of generic and not so generic wall to USB power adapters, some of which work with some devices, and some that work with others, the PS3 adaptor worked with everything. I literally threw a dozen different USB devices at it and it charged them all flawlessly. Victory!
Even though it says it is only compatible with PS3 accessories, it appears to be an actual USB host, which intelligently does a USB handshake with the slave device before charging. The slave device can specify how much load it needs in this handshake, up to 500mA as per the USB standard, the host provides the power, and when the slave device is fully charged, it asks the host to stop and no more power is exchanged.
As opposed to the USB Charging Port, which is simply a "dumb" power port with data pins shorted, this adaptor does a full handshake, and therefore anything you can charge with a PC without special drivers, you should be able to charge with this adaptor. This also won't overcharge your device since power isn't just constantly supplied like in a dumb port. Other users have attested to the same.
Testing with the Sony Reader
In my own experience, this clearly shows when charging the Sony Reader. I have previously charged this device using a UCS standard mobile charger. The charging light immediately goes on and there is otherwise no other reaction from the device (the device does correctly charge).
When using the PS3 charger on the other hand, connecting the charger does not result in the charging light to go on. Instead the Reader turns on, boots up, shows on screen: "USB connected", then "USB charging". At this point, after the handshake, the charging light goes on. When fully powered, the screen displays: "USB charging complete". This behaviour is identical to when you plug the device into any other full USB host such as a PC.
Notes & Conclusion
Because the PS3 adaptor is a standard USB 2.0 host, it only gives up to 500mA as per the spec. There are 2 USB sockets in the adaptor and each is rated at 500mA, however those cannot be combined to output 1000mA, unlike the dedicated charging stations.
Therefore charging speed for your devices will be comparable to plugging them into a computer rather than a wall charger, and devices outside of the USB spec that require >500mA (eg. the iPad) will not be charged.
This however is not an issue for me. As noted in the original question, my concern is only with maximum compatibility, not maximum power or charging speed. And to that end, the PS3 adaptor works perfectly :)
Computer ports can be Fried if a device uses more than 500mA , chargers range from ~500mA to some higher than 2A. The devices itself use a 5V input, but the amount of current they can need to run (even) or get a charge going, or a fast charge going, is more than the normal computer port can handle usually.
Take a device that is designed to power or charge with USB connect, or USB wire, someone is going to shove it into a computer. Be it mini, or micro, or just came with a USB adaption wire. Even if they can find an adaption method, someone will shove it into a computer :-)
At first , things were easy, small MP3 players, charge a phone overnight, small devices with small processors, all able to be "functional" with a simple USB within the computers 500mA specs. Stick them in a computer, or a AC 5V USB port adapter, car adapter, or small wired charger and wait.
All this changes, as portability becomes people lives. They want more power, more speed, more time, and , power hungry devices, larger batteries , fast charge circuits. devices that can barely operate with the 500mA of current, that is spec for the computer port so the computer is not damaged.
If these devices are all charging properly via the computer, then just get a good quality, fair amperage charging things, don't buy more $4 knock off junk that is weak and low powered, and has poor switching circuits in them.
------------------ Proprietary Special Chargers ----------------------------------------------
Enter the "special" charger. The device Itself (not the charger usually) has 2 methods of charging/running:
1) Within the 500mA specs (save that computer), and Via other methods, minimum car chargers, or simple wall chargers.
2) Outside of the 500mA specs: Via special chargers , special car chargers, and special wall adapters with more power. Everything still needs to connect up the 2 Power wires + & - But it doesn't necessarily need the 2 data lines.
This is where the special comes in, via the proprietary chargers.
Trick A) The 2 data lines are not needed when there is no data. Using the data lines in the special chargers, they tell the device that it is On the Special charger, so the device can use more power. Many devices use a few resistors in there, that tie the data lines in different ways. One method just connects the 2 data lines together. one puts in some resistance tying the data lines to the power lines (slightly).
Trick B) I don't know trick B, But they could do about anything, increase the voltage, send simple pulses that indicate , someday they will send an ID out, and status data and it will BSOD :-) , whatever they dream up that can tell the device what it can do , usually it isnt that hard for a electronics geek , to discover it.
Trick C) Add the device having to Also know it is hooked to a computer, to even do computer charging. http://forums.ilounge.com/ipod-nano/209497-why-dont-generic-usb-chargers-work.html
The manufactures point IS many times to purposefully make it proprietary, so you don't use cheap junk on it , so they can control what occurs, so it works when you buy it, so it can cope with what they are trying to do. So it doesn't burn out the computer or other USB things. because there are so many "standards" and so much cheap junk. And of course to Sell-U-Chit.
Software Setting Some of the portable computer devices now can also be set internally to fast charge or not. I have not seen this change the compatibility Or be about special chargers, although if your having power problems with a cheap car adapter that can not output enough power , it might help.
The new 3.0 USB ports are made to handle ~1000mA and they tell you to use max 900mA , so they don't get fried like the old ones did .
What to DO? when it uses a Special charger
Many of the electronic methods for Specific devices are posted on the web, they can have the exact specs, or can indicate what works close enough to have it work ok, even DIY changes you can make yourself with some soldering skill.
Most (not all) of the methods are backwards compatible, they will not destroy another device, they will usually charge another device, at least when the device is off, they just might not charge quickly.
Before mixing things up I Check the Voltage, is it the same , I check the amperage of the charger (it is usually on them), is it very similar. Is it using a standard plug on the device that is sure to be jammed into a computer. Does the manual indicate anything about the specs.
After having a good idea of what is going on I just test things on the devices. I cant tell you to be mixing them up though. You have to make smart careful choices on your own.
In most (not All) regulated 5V input devices, having a higher amperage charger does not hurt them, the voltage sets the "drive" the "Potential" the "force" as long as it is not too far off voltage, the regulation (or lack of) will keep the device from being damaged. If I had a 3A (3000mA) 5V regulated charger, most devices would not draw 3 amps off of it.
In Most , Putting a much higher voltage into the input that is designed for 5V, will destroy the regulation circuit. even if the current is lower (charger cant output enough), when the current consumption slows down the voltage will raise damaging the regulation circuits. It is more critical to have the proper voltage.
What will this do to my batteries? Your Li-ion batteries will die in a few years Just like they did before :-) nothing will change there. The regulation circuit on the device, and the protection circuit on the battery control the current and voltage going to the battery. When screwing this up, it is more likely that you will kill a circuit than a battery. When you dont have the right special charge going, it is more likely that you wont charge the battery, not that IT is damaging the battery.
Why do cheap junk chargers fail to charge. They are overrated, look at the label, see any regulatory requirements to sell that :-) If the charger cannot keep up with the power needs of the device, they charge for a bit , over heat, charge a bit, overheat. The amount of power the device is needing, changes how they act. Normally a magnetic transformer style charger would just do what it could , then its voltage drops, a switching without current control will keep trying to hold the voltage, even if the chip can not handle the draw. A cheap junk charger that is rated for more power can help, assuming its overrated specs are any better.
In my experience, it's primarily an issue with Sony devices. Most USB devices are technically non-compliant with the USB standard, relaxing parts of it for practical reasons such as for simpler charging. The key issue is that a USB device is technically not supposed to pull more than 100 mA (or 150 mA for USB 3.0) until it negotiates with the host for more power. However, most of the devices I've used will simply pull as much power as they can or need, and most USB hosts and chargers have no problem with this.
On the other hand, I've noticed that Sony has a tendency to go to great lengths to ensure their products comply with the USB standard word-for-word, even if this means they won't charge when plugged into a USB AC adapter. Consequently, the PSP is one of the very few devices I have that bear the Certified USB logo on the box.
Even a USB battery like the Sony CP-ELS will try to communicate when plugged in for charging, going so far as to present itself to a computer as a human interface device. It will charge if plugged into a "dumb" charger, but only after it confirms that the charger is truly incapable of USB communication (it will not charge through a USB hub connected to a USB wall charger, for example). The PS3 controller and PSP refuse to charge from USB unless they can communicate with a host and specifically negotiate for power.
In short, I just don't think it's necessary for Sony to do this. Consumers don't actively look for the Certified USB logo, they simply expect their devices to charge when plugged in.
To answer the question, what you need is a USB charger that can act as a full host capable of communicating with devices, such as the one you described in your own answer.