I have a ThinkPad T440 that came with the new adapter plug "slim-fit". The original charger is 19V, 3.42A. I ordered a replacement AC for travel, and Lenovo sent to me a charger that is 20V, 4.5A, with the same polarity. I'd want to ensure that it is totally safe the use the new one with higher voltage and current rating. From what I have read on various forums, they say it is OK to use the new one. Is it safe to go ahead and start using the 20V, 4.5A one?

  • Only Lenovo can definitively confirm that it is compatible and not a shipping mistake, and a quick call or email to their tech support or customer support will do that. However in general, a 1 volt difference for something designed for 19 volts should be fine. It will create an extra few watts of heat that must be dissipated, so make sure the ventilation area is clear. – fixer1234 Oct 25 '14 at 14:29
  • Thanks for the feedback @fixer1234. I contact Lenovo and really there's no one who barely knows more than me to say with confidence. About the 19V/20V I agree with you, should be fine, but my really question is about the new AC with the $.5A and the old one with 3.42A. About that, what do you think? Thanks again. – andremartins Oct 25 '14 at 16:52
  • The current rating tells you about the capacity to provide power. A 4.5A charger can support a higher power requirement than a 3.42A charger. The chargers are manufactured to be generic--same charger provided for multiple machines. They generally are not used at full capacity. The 4.5A charger would have more unused capacity. If the actual current draw is a tiny fraction of the rated capacity, the voltage could be off if the charger is not well designed, but if it is a manufacturer-supplied charger, my guess would be that your usage would be within the design specs for regulating voltage. – fixer1234 Oct 25 '14 at 17:03
  • @fixer1234 thanks again. I have more confidence to use it with my T440. Awesome explanation. – andremartins Oct 25 '14 at 17:15

Yes you can use it. At such voltages an 1V difference isn't much (it would be dangerous at a lower voltage though, an extreme example would be a nominal voltage of 1V and you give it 2V instead, in this case it's the double and can very well damage the device).

I've personally used a Thinkpad T60 on 26V instead of 19V and never had any issues, same with my current Dell E6400, so an 1V difference is nothing compared to that.


We got about 10 of these same adapters around our office.
They are used daily with T440 and X240 without issue.

The extra current is perfectly fine. The circuitry inside the laptop determines how much current is drawn. And it will only draw as much as it needs. It only means that the adapters maximum capacity will not be fully utilized.

The voltage difference is well with the variation acceptable to the laptop.
Typically the voltage may vary from 5% to low up to 10% to high.

20/19 = 1.0526
Slighty over 5% is nothing to worry about.

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