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I was wondering if today's laptops and adapters together with power cords can be mixed and matched?

For example, my laptop is Lenovo T400 and its adapter outputs 20V and 4.5A. In my office, there is another laptop's adapter which outputs 19V and 4.3A. I was wondering if I forget to bring the adapter with my laptop to my office, will it be all right to use the other one instead?

What are some principles to tell if an adapter can be used by a laptop?

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The answer is "generally if they're close enough, yes, but you do this at your own risk". Laptops generally have some tolerance in the incoming power that they'll accept so you'll probably be alright with something that close, but it can cause anything from odd behavior to outright damage. (Personally, I'd just buy a second adapter and LEAVE one at the office...)

The best thing to do is look online and see if other people have reported problems, but you may have difficulty finding somebody with the same model using the same wrong adapter. I have no experience with changing T400 adapters but I'm GUESSING you'd be okay here. That's just a guess, though; you won't know until you try. Just don't let the smoke out...

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  • Thanks! What are some principles to tell if an adapter can be used by a laptop?
    – Tim
    Commented Apr 11, 2011 at 23:43
  • Unfortunately there is no hard and fast rule of thumb that I'm aware of, unless the manufacturer explicitly says 'anything that meets <X> criteria is okay'.
    – Shinrai
    Commented Apr 11, 2011 at 23:52
  • lenovo seems to use fairly non standard power adaptors, and that's another thing you'd need to look out for.
    – Journeyman Geek ♦
    Commented Apr 12, 2011 at 0:07
  • @Journeyman: in what aspect is it nonstandard?
    – Tim
    Commented Apr 12, 2011 at 4:15
  • slightly larger plug om the post IBM models than anything else i've seen
    – Journeyman Geek ♦
    Commented Apr 12, 2011 at 8:42
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Generally it is a bad idea, you need to have proper voltage and amperage, otherwise you will cause damage. It is true that there is tolerance for slight variances, but laptops can vary greatly (for example, some take as low as 14v, others as high as 20v). Even if it is the same plug type, if you plug in the wrong adapter, over time it will do damage. The same goes for amperage. There is a distinct difference between 1.5 and 3.5. You can have an adapter that feeds 18.5v and 1.5 amps and if you plug it into a laptop in place of one that fed 19v 3.5 amps, you will definitely cause damage, even if the voltage is close. Be very careful when selecting alternate power adapters.

With that said, in your particular case, it is very close. 1 volt is not a huge difference, but over a long period of time, the variance in force can potentially cause damage to the motherboard. It is usually healthier to have a bit more than a bit less.

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Look like a lot of us missed these points:

  1. Volt: it is only allowed +_5%

    That is, if your specified adapter is 20V you can use an adapter with a voltage range from 19V to 21V only.

  2. The current must be enough within this voltage range to produce the watts specified for your equipment (by using the formula W = V X A)

    In other words if your original adapter is 20V~4.5A=90W you can use 19V~4.74A (or higher)=90W, or 21V~4.28A (or higher)=90W.

Note that your equipment will only suck the current it needs to yield its wattage on the supplied volt at any given time. In the case of the 90W equipment above, it will only sucks 4.74A of 19V, 4.5A of 20V and 4.28A of 21V from THESE ONLY INTERCHANGEABLE adapters for an OEM 20V 90W adapter irrespective of how much current the adapter is capable of supplying.

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