Can the N3 /w Ethernet be powered by an external device?

I normally design involved hardware which makes use of both an N3 (Ethernet ) and this gadget from a different company, Board of Education Shield (for Arduino) since it has an attached breadboard an a Prototype Shield with a small breadboard similar to the one on that thing. The problem? When the board is attached to the host via USB the stuff on the top doesn’t run at all. It only works properly when the barrel connector has an external power supply attached,.
So the question is, "Can I do that, and still develop programs and send them to the unit via USB?

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If I understand your question correctly, yes, you can have your Netduino connected to both a power supply and USB. It will only use the USB to power stuff if it doesn’t already have power from the barrel connector.