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I've got two cables that connect a laptop to the electric wall socket.
The original that came with the laptop is bigger and the sticker with the specs says it outputs 19v - 4.74A.
The second smaller one only does 19v - 3.42A.

I'd prefer to use the smaller one for mobility reasons, can there be any downside to doing so?
In short term, it works well, might it be a problem in the long term use?
Will it affect the battery charging or lifespan? can it be dangerous to the rest of hardware in any way?

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up vote 3 down vote accepted

Addition from Richard Hoskins' great comment below:

Worst case failure could be that the AC adapter catches fire. When it comes to power delivery, it is best to be conservative and not exceed manufacturer's specifications.


By using the AC adapter which can output lower current than the one supplied with the laptop, you are running the risk of your laptop pulling more current than the AC adapter can handle. If that does happen, likely failure would be:

  • The AC adapter would quit working by tripping over-current protection
  • With the high current causing the temperature to rise, the AC adapter could physically break.

With that said, you are likely OK especially if the temperature of the AC adapter isn't hotter than the original. I just wouldn't leave it plugged in over a long weekend running software that pulls maximum power. If you do plan to do so, test doing it under supervision first. :-)

It depends upon what the input requirement is for your laptop and the specs of the AC adapter. From the specs given, you may be at risk of the second (smaller) cable failing. Does the smaller cable get warm at all?

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The cable itself doesn't get warm, as for the adapter, both get warm to a reasonable amount, the smaller not in an alarming way, as far as I can assess. Then again, I'm not sure I trust my warmth assessment skills. – Eran Sep 3 '09 at 2:00
Is there anyway I can find the laptops requirements, the manufacturer's site doesn't list it. (I've got an MSI EX600) – Eran Sep 3 '09 at 2:04
Oh, so it is the adapter with the specs mentioned. What is the input requirement for the laptop? If you can give the brand/model, I can try to look it up for you. – hanleyp Sep 3 '09 at 2:05
I = P / V so, I = 90W / !9VDC, or 4.74A. Like the supplied walwart. Me personally, I wouldn't use anything smaller. – Richard Hoskins Sep 3 '09 at 2:44
A failure mode not mentioned in this answer is fire. The walwart could catch on fire. Overvoltage protection does not always work. Cheap Class 3 electronics do not always have overvoltage protection. Cost cutting concerns in factories frequently result in a product that doesn not even meet the advertised specification, let alone have any play on the high end. It is just not worth it. – Richard Hoskins Sep 3 '09 at 4:21

run a stress on the smaller PSU without the battery, if the laptop remains in stable condition and the PSU doesn't get too warm, it should be OK to use.

if it only works stable with the battery, then there is a drawback: if the PSU doesn't provide sufficient power then the laptop will drain the battery even while connected to AC and thus knock off precious charge/dischage cycles, which are limited in their number with lithium ion batteries.

disclaimer: you do this at your own risk and i will not be held responsible for any damage caused by using a supply not approved by the manufacturer :)

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Interesting idea, I might try that. :) – Eran Sep 3 '09 at 2:17
Testing under supervision is a good thing to do. My understanding of an AC adapter is that it could be able to output more power than rated for short periods of time unless the over-current trip point is tight. – hanleyp Sep 3 '09 at 2:24

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