Will leaving the ac adapter plugged-in without the laptop attached harm the adapter?

Every manual I've ever read recommends promptly disconnecting the ac adapter when not in use.  I've seen quite a few people leave take their laptops and leave their ac adapters still plugged-in.  In fact, my brother does this all the time.

Is it a fire/shock risk to leave it plugged in?  Can it be a damage the adapter?  I'd love to leave my adapter for my laptop and  cell phone plugged at all times as the power strip I normally use is quite unaccessible.

Can't really get a straight answer for this.  If it is safe, are all these manufactures just blowing smoke?

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Have you ever touched one while it was still plugged in to the socket but not the computer. Some of them can get real hot just sitting there.
I would take the manufacturers advice. Why risk not taking their advice? What possible gain would you get by not unplugging it?
I have never heard of an ac adapter going bad just because it was left plugged in.  But reasons for the manufacturer telling you to disconnect when not in use:  

1) You might leave it there, if you have a laptop, and if it's a place you're never going to visit again, it's lost.  

2)It is also still acting as a transformer, so the power lead is still providing current when not connected, and that is a fire hazard if it touches conductive material.  

So it is a good practice to unplug it if it is going to be left unattended, but I think the probability of it starting a fire is low.

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In July 2001, Apple® Computer announced the recall of 570,000 AC adapters worldwide sold with PowerBook® G3 laptops from May 1998 until March 2000. The adapters were recalled because of a fire risk.

In cooperation with the U.S. Consumer Product Safety Commission, Compaq Computer Corporation announced a worldwide voluntary recall and replacement program for approximately 1.4 million AC adapters used with certain notebook products. These AC adapters can overheat, posing a potential fire hazard.

Dell recalls notebook batteries suspected of fire hazard
The giant PC maker recalls as many as 27,000 notebook batteries suspected of causing fires--the second major problem the company has had with portables this year.
October 13, 2000 5:30 AM

There is a recall for SOME of the AC adapters (power cord) that were packaged with TTI Laptop computers.
These AC adapters can overheat, posing a potential fire hazard. Please check your AC adapter and see if it has one of the following "model series #":PPP003SD PPP003 PP2012

Bizcom Notebooks
 A design vulnerability in the supplier's battery pack, in combination with a manufacturing-process flaw in their battery pack assembly, can subject the battery to overcharge, potentially leading to excessive heat and possibly fire. After thorough analysis, the battery pack design issue and manufacturing-process flaw have been corrected.
 We are recalling about 13,000 batteries sold with N30W and N38W2 series notebook computers, or provided separately in customer kits or as replacement batteries for these systems. The Recalling is only for Battery, it has nothing related to Notebook base unit itself and impacted battery can be identified by a small colored label on the rear of the battery.

Ford engineers discovered in pre-production crash tests that rear-end collisions would rupture the Pinto's fuel system extremely easily.

I think it is simply a case of the manufacturers protecting themselves. If a fire occurs, and you haven't pulled the plug on the adapter, they will be absolved of all blame, as you didn't follow the instructions.

From a practical point of view, the heat dissipation is energy wasted, which is bad in general, even if it does not mean a fire hazard. And you pay for your electricity, don't you?
I knew the Pinto analogy wouldn't be understood :)

I was initially puzzled at that, but then I realized that some manufacturers sell defective or badly designed products all the time.  It's a matter of not wanting to give up those dollars, at someone else's risk.  Did I understand you correctly?

With regard to laptop chargers, I think a faulty one would give indications of being bad early on (burnt smell, lots of heat).  After you've used it once, you would probably be reluctant to use it again.
The problem may be with users not recognizing "too hot".
40C feels warm and 60C feels hot while 70C may be a safe working temp for whatever unit we're discussing. How to know when your laptop power brick is going on an incendiary tour?
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