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I purchased a spare power adapter for my ASUS Q500A laptop. When I received it, I checked the specs and found that they differ than the OEM adapter. The OEM input is 100-240V 50-60Hz 2.0A. The spare input is 100-240V 50-60Hz 1.2A. Both outputs are listed at 19V 3.42A. Does this difference matter? Should I use the adapter or return it? Thanks...

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  • What pedigree does the adapter have? Is it from a known company or something else? Jun 20, 2014 at 20:36
  • Yes it "matters" but not in the sense of not-working. Many Dell laptops (for an example) will take either of 2 different power adapters, 65w or 90w. Provided that everything else is the same, the only real difference is that the 90w tends to charge up faster. In my own experience, the side-effect is that the 90w adapters also tend to last a longer time. Typically the larger adapter also costs more.
    – Debra
    Jun 21, 2014 at 2:45
  • possible duplicate of Laptop power supplies, does current matter? Jun 21, 2014 at 15:10

3 Answers 3

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Your original OEM adapter had a poor power factor. 2.0Amps * 100V is 200 VA of apparent power. Apparent power is the maximum amount of real and imaginary power. Real power is delivered to and absorbed by the power adapter. Imaginary power (or reactive power) is power that must be drawn in by the power supply by capacitors or inductors and then sent back to the grid.

Usually laptops take either 85 watts or 65 watts. The output of both of those adapters says they are 65 watt adapters. I don't see any issue at all with the after market adapter. If anything it has better power factor.

Power factor is the ratio between real power and apparent power. Ideally, your PS should have a PF of 1. In your case, the OEM adapter looks to have a PF of 65/200=0.325 (ignoring losses). Your after market PS has a PF of 65/120=0.54. One reason PF is important is due to the extra losses incurred by the extra current necessary to drive poor PF devices.

Lastly, if somehow the aftermarket one isn't able to produce 65 watts, the only downfall you'll have with the aftermarket adapter is that your battery may charge slightly slower.

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It sounds like the power adapter you bought will work fine. The output voltage and current capacity are what's important, as that's what your laptop will see.

If you want to be extra sure, you can also check the polarity on the barrel plug. Just take a voltmeter and make sure the voltage on the old plug is the same polarity as this new one. It's almost certain that it will be the same, but it doesn't hurt to check.

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Perhaps you have seen or heard the spark, plugging some chargers into AC. This is due to the storage capacitance on the primary rectifier. Some suppliers may incorporate an NTC surge suppressor or a different Converter method, which can reduce this breaker rating .

When you see a product label with power specs that show only input V & A and not input V, A & W, people often assume incorrectly that you can relate V*A and infer efficiency. This is not the case. Current ratings for input are only for breaker ratings in planning how many devices may be connected safely to properly sized wiring and breaker. This is based on Electrical Codes and safety laws, not efficiency.

Both will perform well.

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