Can you charge the Asus Transformer (or the newer Prime) without the keyboard dock?
Since the tablet itself does not have any USB ports, I don't see how you could charge the tablet without the dock or a very clunky proprietary charging cable. However, It seems insane to manufacture and market a high-end tablet that can't charge without a giant peripheral (and sell/price the thing independently too).
Am I missing something? Or, is Asus just insane?
It comes with an AC adapter and a charging/data cable which can plug directly into the tablet, though it does still use their proprietary cable connection since it plugs into the same connector that the keyboard dock uses (the other end is male USB).
Using proprietary charging cables is not unheard of - Samsung and Apple have done this; I don't personally like it when companies use proprietary cables, but in this case it's mostly because the charging/data port doubles as the dock connector.
Here's an image from Engadget's unboxing/review of the Prime. The AC adapter is at the bottom.
As others have pointed out, the Transformer does require a proprietary cable for charging. There are a couple of drawbacks to this.
I am not sure why Asus went with a proprietary cable for charging. I suspect it's because that port is meant to be a multipurpose port for the dock, charging, and accessories, and that using a proprietary port makes all that much easier. However there aren't really any accessories for it and anyway they could have included a micro-usb port along with the dock/accessory port.
In any case, you would still need the wall plug adapter because of the higher power requirements for charging this device.
I think the proprietary charger is needed because of the higher voltages required by the dual-battery design. I guess you could use the regular usb connector, but it might annoy people when a regular cable did not work because it does not provide the right voltages. Using the odd connector ensures that the correct charger gets used.
From what I can see, the transformer charger works much simpeler. If you look closely into the USB connections, you can see an extra set of five pins. At the charger USB socket, a pair of these pins supplies +15V to the tablet. References on the net state that is OK to connect a +12V source to the USB power pins.
Most of these answers are correct as far as they go.
You CAN charge the ASUS Transformer without the base using any standard USB source (computer, plug, etc) with the proprietary cable. The Transformer needs to be off or at least have the screen blank in order for this to work, and with less than 10 volts it will NOT indicate that it is charging...but it is, albeit very slowly.
The included wall charger uses pin 3 of the USB to determine if it is connected to an ASUS transformer or another device. It supplies 15 volts if connected to the Transformer or base, and 5 volts to any other device so it can be safely used to charge a phone or other device.
Many people have successfully charged their transformer with a direct connection to a 12-volt source like a car battery. The positive terminal needs to go to USB pin 1 (red wire) and the negative to the ground at pin 4. BE AWARE THAT WHILE THIS WORKS, IT MAY VOID YOUR WARRANTY. Such a charging setup CANNOT BE USED FOR PHONES OR OTHER DEVICES!
I've tried several third party "generic" 2.1A chargers (AC and DC) with the proprietary ASUS supplied cable and all of the chargers DO NOT work with the ASUS TF300T tablet. As stated above, you need both the proprietary cable AND proprietary charger to charge. Very disappointing.
With the big push to the micro-USB standard for all cell phones to be more green (don't have to throw out the cables/chargers with each new phone anymore), it's irritating to find a tablet that doesn't do the same. Now, you have to the proprietary charger/cable around and it wont charge with the 2.1A car chargers.
Perhaps there is a technical reason and not just wanting more money from customers to buy the ASUS charger.