Hi all,
here are some facts that might interest you:

Other than the "old" serial SX-Key which was powered from the target SX system, the "new" SX-Key USB is powered from the USB port. This has some advantages:

1. Like its predecessor, the SX-Key USB requires a 5 Volt supply in order to operate correctly, and to generate the 12 V programming voltage. As the 5 V supply comes from the USB port, the target SX system may run at a lower supply voltage, e.g. 3.3V without the need for a special adapter, like the (no longer available) SX-Ring.

2. When the target SX system was powered down during a running debug session with a serial SX-Key, the IDE reported a "Chip connection failed", or "SX-Key not found" error, and closed the debugger because the serial SX-Key also lost power in this case, and the IDE could no longer communicate with the SX-Key. With the new SX-Key USB, the communication between the IDE and the SX-Key remains intact, even with the target SX system powered down. In this case, the debugger enters the "Sleeping" state which will change back to "Idle" as soon as the target SX system is re-powered again.

3. When you do a target hardware reset, e.g. by pressing the reset button on the SX-Tech Board, or the Professional Development Board, the Debugger enters the "Idle" state, and you can restart debugging by clicking "Step", "Walk", or "Run" like after having clicked the debugger's  "Reset" button.

Have Fun!

Thank you for pointing out these tips Guenther.

Is the USB SX Blitz also powered by the USB power?

Hi William,
to my knowledge, it is not.

Can the USB SX Key program an SX chip that is totally not powered?

No, it can't. The SX-Key USB is powered from the USB port but this supply is not fed through to the target's Vdd. Therefore, you need a separate power supply for the target as programming only works when the target SX is powered up in order to communicate during the programming process.

Does this mean that the Vdd pin on the the SX Key USB is unused?
Can we modify the SX Key to provide 5v to the Vdd pin?

Yes, the Vdd pin on the SX-Key USB is not connected. This is why this pin is marked as "----" instead of "Vdd" on the SX-Key USB.

I can't really recommend modifying the SX-Key USB to provide 5V to the Vdd pin. Yes, you migh place a wire jumper from the Vdd pin to some pad on the board connected to the filtered 5V coming from the USB port. You would have to remove the shrink tube from the SX-Key to do that, so you would immediately void any Parallax warrantee. In addition, the USB port might get overloaded depending on the current drawn by the target system.

If you plan to build some kind of USB-powered SX programmer, it should be ok to draw the additional supply for the SX to be programmed from the USB port. Nevertheless, you would have to modify an SX-Key USB out of Parallax warranty as mentioned before.

Probably a better solution is to buy a ZIFF socket (about $7) and build a small board with a resistor, an LM2940CT-5 power regulator($1.25), 22uf tantalium capacitor ($ 0.30), a 0.47uf capacitor($0.22), a power connector 2.5MM male jack ($0.20), a 10K resistor ($0.01) and 0.1 uf capacitor ($0.20), 4 male header pins.
If you have another board that already regulates the power, you can leave off the LM2950, 0.47 cap, 22uf cap, and 2.5MM plug. Simply jump the power across, then the board becomes real simple.

I've included pictures for you (it's pretty easy to do). I also use this as a quick test board, which is why I have the extra pins.

William,
Modifying the SX-Key to power a project through the programming/debugging header is a solution looking for a problem.  Unless you plan on always having an SX-Key and a PC attached to your project, at some point you need to have an external power supply for the project.  If so, just attach it to the project at the start and do something productive with the SX-Key.