I have a 168 and 328 Stalker. I have been using the 168 Stalker with a 5vdc Arduino power supply connected to the JST connector without problems.
I tried using the same power supply with the 328 and it would not power up. I measured the voltages on the 5vdc pin and measured 3.143 volts. I then powered the 328 with the Uart_SB adapter and it worked fine and the 5vdc pin measured 4.97 volts. After reviewing the Stalker documentation, it indicates that the voltage for the JST should be 7-12 vdc which is higher than a standard Arduino power supply. I then tried powering the 328 with the JYE tech ocsilloscope 9VDC power supply and the Stalker operated properly then. Even with this power supply the 5vdc pin only measured 4.53 volts.
It appears that the onboard power controller does not regulate power very good and might be the reason some users have had problems with the SD card and Xbee. If other users are having any problems with their Stalker, they might want to check the voltage on the 5vdc pin to make sure there is enough power available.
It looks like it might be better to power the Stalker from the Uart port. Does anybody have recommendations for a safe power supply that can be used? The standard Arduino power supply puts out 5.21 vdc but I’m not sure it is safe to connect it directly to the Uart port.