engineer_comp_geek got this one right – companies in the industry make a lot of money by having a non-standard power adapter, which you can only buy from them (at a high profit margin). The same scam is also behind portable devices that use proprietary rechargeable batteries rather than a standard size.
Notebooks are usually expensive enough that cobbling together a PS is usually not a great idea. What is the specific model of the notebook? Replacement PSs can often be had very reasonably on EBay
True except higher mA units trend linearly with the higher voltage rating, not the other way around. Be careful using a generic 500mA unit where a 200 mA unit is indicated, this is asking for trouble all things being equal; It’s better to under supply the voltage to the device (with reason) if the device isn’t loaded down enough the power adapter will typically smoke same, as you noted they are not regulated.
Well, I think that’s the main lesson I learned from all of this. There’s a big difference between the low end and high end AC adapters and it would have been a bad idea for me to have used some old adapter that I found in my discard box just because the plug fit and the specs were about the same.
I went ahead and ordered one off the Internet for about $33 including shipping.
This thread has been very informative for me, and I appreciate everyone’s input.
One last question while I’ve got you here.
Is it fair to say that all electronic components - stereos, TV’s, dishwashers, whatever - have something like an AC adapter built into them? Perhaps as part of the power supply?
Pretty much.
It depends on the device. The simplest devices are incandescant lights and heaters. Those don’t generally care at all whether they’re AC or DC, or what the waveform is. All a heater or incandescant light bulb (which is really just a heater, itself) cares about is the average power. Then you have motors: A motor can be designed to use AC or DC, but not generally both. So if the motor is the only thing in an appliance that needs power, it’s probably simpler to just make it an AC motor in the first place, and not bother with an adaptor. An AC motor will be designed for a particular frequency, and if you hook it up to a higher or lower frequency, it’ll run faster or slower than it’s supposed to, and may not work as well. But motors will generally be pretty tolerant of messy waveforms, so long as they’re negative half the cycle and positive half the cycle. Finally, you have your solid-state devices (basically anything with transistors or diodes in it). Those generally have fairly specific requirements, and usually use DC (though digital clocks often get their timing from the AC frequency, and will run fast or slow if given the wrong frequency). So those will need a power adaptor, and specifically the right power adaptor, as discussed in this thread.
By definition, “electronic” excludes things like incandescent lights and motors.
Because they don’t know the words?
However, a simple triac-based (or SCR-based) dimmer for an incandescent light would be an example of a device that is definitely electronic, but doesn’t involve anything resembling the OP’s “AC Adapter”.
More complex dimmers (e.g. timed, remote-controlled, or X10) would need a DC power supply, but in many cases a transformer wouldn’t be necessary since electrical isolation may not be important, and non-isolated step-down switching semiconductors are cheaper and less bulky than a transformer.
And also most dishwashers, but El Zagna included those on his list. So I figured he was using a broader than standard definition of “electronic”.
Nitpick, but DC or AC & AC frequency do have considerations in incandescent bulbs. Not for the actual luminescent functioning, but for the life of the bulb. Light bulbs intended for AC use generally have some additional supports for the filament, in order to dampen vibrations caused by the AC, and prolong the life of the bulb. DC light bulbs can get by without this.
O.K., my turn to nitpick. 
-
Chronos said they don’t generally care. I’m sure he knows there are small differences between AC & DC when powering a light bulb. But he also understood those differences were not relevant to this discussion.
-
The supports *damp * vibrations, not dampen.
This thread is very interesting as I always wondered what went on in those little plastic boxes. From the comments above, I think I understand how they work, but I have some questions.
If I have this right, the basic wall wart is just a transformer and a (1 or more diode) rectifier with appropriate capacitors, etc. to smooth the supply. 110v 60Hz AC current (in the US) from the household service is sent into the transformer, and depending on the windings of the transformer, the desired voltage 60Hz current comes out, which is then run through the rectifier to get DC of the desired voltage (proportionately subject to the variations in the input voltage). I assume that if you plug these into 240v AC current, you will get roughly double the output voltage.
My question on this type of basic wall wart, is how much, if any, current do they draw when they are plugged in to the wall but the appliance on the other end is drawing no current. I normally leave my cell phone, iPod, etc. chargers plugged in to the wall, and periodically attach them to their respective devices to charge. Am I wasting electricity doing this?
Switching to the switching supply, I gather that the 110v AC input is immediately rectified to 110v DC, which is then fed into a chopper, which produces a high frequency 110v square wave AC. The high frequency AC is then run through a transformer, rectifed and smoothed to get the appropriate DC voltage.
I suppose I should again ask if this type of power supply (which I assume my laptop uses) draws current from the wall if the computer is unplugged or switched off.
However, my more significant question is how does this type of converter accept input voltages ranging from 110v to 240v and produce the constant output voltage my laptop needs?
Interesting discussion!
I have a question or two myself.
Let us speak of the computer you are currently sitting in front of.
How many ‘wall warts’ are involved in your configuaration?
Counting my phone and speakers I have 5!
Will someone, one day, invent a universal transformer station to replace them all?
Like a power bar but a transformer instead, for whatever peripherals you acquire.
Meeting all your transforming needs in one handy universal unit.
Just to add to what’s been said about this, often the reason a particular small solid-state device, such as a stereo component, weighs what it does is because of a big fat transformer inside the case.
Why?
Main Entry: 2damp
Function: verb
transitive verb
1 a : to affect with or as if with a noxious gas : CHOKE b : to diminish the activity or intensity of <damping down the causes of inflation> <liquid damps out compass oscillations> c : to check the vibration or oscillation of (as a string or voltage)
2 : DAMPEN
intransitive verb : to diminish progressively in vibration or oscillation
If you want to nitpick further, a typical light bulb isn’t going to run as designed if fed 0.1 Hz AC, either ;).
Just to throw in - I am greatly enamored of the power jack on the new MacBooks - a small pit on the back of the laptop and a small magnetic block on the end of the cable - obviously with appropriate conductive pads. Such a simple idea, but so cool. If only they were not so expensive 
If you trip over the power adapter, the laptop will not come crashing down - the cable pulls out. With the trend to wireless peripherals the chances of your laptop getting killed by someone standing on a wire is going down all the time.
Actually, my laptop is a bit like this - I use a 3rd party generic adapter on the road. To allow you to select the appropriate end for the cable, you have attachable plugs. If I trip on my cable, that end is likely to pull out before the laptop slides off the table - an unintended feature I am pretty grateful for - I use my laptop for live music and there are too many people and cables about for comfort.
Si
I don’t know; perhaps a small amount. We have a power analyzer here at work. Maybe I’ll hook one up and measure the real power of a wall wart with nothing plugged into its output.
The DC voltage is higher than 110 V. It’s usually between 150 VDC and 170 VDC, depending on the load.
I may be wrong about this, but I believe some larger switching power supplies have a sensing circuit on the input. When it senses 120 VAC it configures the rectifier as a voltage doubler. As for smaller supplies, I believe they simply don’t care about the input voltage (within limits). The mains are converted to DC, and the supply “simply” regulates the output voltage by varying the duty cycle of the MOSFET.