9VDC Power source plugged in while USB connected, Uno, any issues?

I was just curious if there would be any conflict with having a 9VDC power adapter plugged into the power receptacle, while the USB is connected to a PC.

Are they somewhat isolated? The 9V would not get into the USB 5V?

http://arduino.cc/en/Main/ArduinoBoardUno

Power section, first sentence.

First sentence:

The Arduino Uno can be powered via the USB connection [u]or[/u] with an external power supply.

Sorry I also read this, but it does not answer my question. I suppose it will be fine.

Sorry. Meant read the first AND second sentence.

Wow.

That page isn't very clear even reading all the sentences. I've had both plugged in quite happily

The power source is selected automatically.

That tells you both can be plugged in at the same time. Edit: Fair enough.

Yes. You can plug in a source to the barrel jack and USB at the same time.

[quote author=James C4S link=topic=155662.msg1167677#msg1167677 date=1363962360]

The power source is selected automatically.

That tells you both can be plugged in at the same time.

[/quote]

No, it doesn't... it's ambiguous. When I re-read it in the light of this thread, I took it that it can mean you can use either source, and it'll know which one is plugged in. It doesn't actually say that it will select one of the two when both are plugged in.

If both voltage sources are available it selects the external voltage source and isolates the USB +5vdc voltage.

Lefty