DC Current Sensing / Detection

Maybe use some sort of relay: on the switch side of the relay hook it into the line that will feed power through the connector, on the pass through side of the relay hook up +V to one leg and the LED to ground on the other leg.

Just a quick suggestion - don't even fully know if it will work or not (seems like it would work in theory).

Maybe someone else will have a better suggestion...

Edit: I just remembered about NPN/PNP transistors from way back in a very basic electronics class that I took a long time ago. Maybe there's a way to add a NPN transistor to the wiring of each outlet with an LED/resistor off of one leg of the transistor to ground. Maybe this will give you an idea about it: http://www.cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html

That class was a very long time ago though, so take it with a grain of salt... :P

To indicate current draw, you'll need something that senses current in series with the circuit, that's basically what an ammeter does.  However, without knowing the amount of current it's difficult to implement this.  Basically, you'll need a small amount of resistance in series, and measure the voltage drop across it as a result of the flow of current.  When that voltage drop exceeds a certain pre-determined threshold (perhaps done with a comparator), it turns on an LED.

But the appropriate amount of resistance is current-dependent.  Too little resistance and there will be hardly any drop to measure, and too much resistance may cause the resistor to overheat/burn up and overload the sensing circuit.  Also, the whole concept of voltage drop means that load regulation is compromised, if that matters.  If the current draw will be dynamic and vary over a wide range, then it makes things even more difficult.  This is why general purpose ammeters have multiple selectable ranges (either manual or automatic).

How about -

1) use a small value sense resistor (take 100 milliOhm as an example) in series with the supply line

2) put an instrumentation amp (like the Intersil EL8170) across the sense resistor.

3) let's assume the threshold current you want is 20 mA down the sense line.  So your voltage drop that you want to sense is 100 millOhms * 20 mA across the sense resistor, or 2 mV. 

4) Set up your feedback network on the EL8170 such that your gain is 400.  So a 2 mV drop across sense resistor is amplified to a single-ended voltage of 800 mV

5) take the output of the instrumentation amp into a comparator.  Have the other comparator input go to a forward biased Si diode.  The 800 mV output of the instrumentation amp will be greater than the approx 700 mV across the diode.

6) Have the comparator output drive your LED.  Have the LED supplied by your notebook adapter, not the rail that you're sensing.

Hope that helps ...