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Yesterday I was studying the BIOS of a DELL Latitude E6420 laptop and enabled notifications that check and warn if the power supply is not appropriate for laptop.

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Immediately I got this message:

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The power supply is authentic DELL's power supply but 65W which is less than recommended as BIOS tells me. How will this impact my system and performance? Is this critical and i need to consider buying 90W power supply or i can live with that?

Intel Turbo Boost boosts up to 2.85Ghz which is less than maximum of 3.2GHz processor can handle. Can it be because of a less powerful power supply?

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Actually less power means it runs your computer generally, but should you try to do something that requires more power, your computer will slow down or crash. –  user93107 Aug 16 '11 at 6:03
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6 Answers

up vote 3 down vote accepted

The reason you have a 65W power supply is because you ordered it. When buying this model, one has several options ranging from 60W to 97W. (65W is not mentioned, so I assume that 60W is the same as 65W).

However, only the 60W version supports ExpressCharge, which is described as :

when the computer is turned off, the AC adapter charges a completely discharged battery to 80 percent in about 1 hour and to 100 percent in approximately 2 hours. Charge time is longer with the computer turned on. You can leave the battery in the computer for as long as you like. The battery's internal circuitry prevents the battery from overcharging.

As far as I could find, many people have chosen the 65W battery model over 90W (example here).

Therefore, I would ignore this BIOS message as being useless. If you changed to a 9-cell battery, you would lose ExpressCharge, so would maybe lose more than you gained in charge-time.

As regarding Turbo Boost, its exact functioning is a great mystery that was never fully resolved. Try to contact Dell Support, who might give you a meaningful answer.

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It will not affect your your performance at all, or at the very least - it should not.

Most laptop batteries are capable of supplying around 20-25 W and that is what a typical laptop draws under normal laod, the added beef behind the power supply is so you have enough juice to run the system and charge the battery at the same time.

Essentially two things might happen. 1. The battery won't charge as fast as it should (first priority goes to giving the machine juice) especially under heavier load. 2. The charger will be hotter than an equivalent 90W one, this will wear it out faster and lower its life expectancy.

As to why you were given a "smaller" power supply. It could be one of several reasons, (in order of likelihood) .

  1. Mistake at the factory - check the packing list in the manual and see if it specifies the model of the charger and see if it matches

  2. Intentional replacement due to engineering changes that weren't updated in the BIOS that shipped originally

  3. A generic BIOS that is using some default value and the actual model specs weren't set properly.

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I believe 90w is correct for the Latitude E6420. I suspect a factory mix-up, the Dell PA-series adapters (which come in a 65w and 90w variant) are all nearly identical to each other and it would be easy to package the wrong one, especially if this laptop ever went to a service center (for example, refurbishment) since that's always more chaotic than the production line. –  jcrawfordor Aug 16 '11 at 6:41
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This is for charging speed. If you power supply is not powerful enough it is possible to actually run down your battery while plugged in (though it will charge when it is turned off, and I do not know if this will be the case with you). I do not know why this was the shipped power supply, but you should get a new one.

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Actually your system will perform worse when a less powered adaptor is connected. I experienced this issue while gaming on my Latitude e6400. I left home for a couple of days and took only 65W travel power brick (I have both 65W and 90W) and observed a drastic performance drop when connected to AC. What is more peculiar the system performs substantially better running off battery when I unplug it from power source. I get around 30->10 fps drop when I plug in the AC back. Changing power plan settings doesn't really affect this behaviour. Still looking for some kind of override but I suspect this to be something at BIOS level and the BIOS itself has only the warning setting.

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This is interesting. You can find accompanying pictures in my question. I have original 65W Dell power adapter and if I have option "Enable Adapter Warning" checked in BIOS, I get to a screen telling me that this charger is below 90W recommended. According to your statement, it provides optimized performance when using 90W power adapter although in my case I did not notice difference when running on battery and AC. Since I don't use heavy applications this could be the reason I did not notice difference in performance. Thanks for sharing your observation. –  Boris_yo Dec 27 '12 at 6:50
    
From an anonymous suggested edit: The behaviour is called CPU throttling, the system can reduce the cpu freq when e.g. overheated. It is also applied in this case - when connected to a 65W brick the cpu freq drops from 3,06 GHz (C2D T9900) to 0,52 GHz. You can override it with software like RMClock. –  Dennis Jan 1 '13 at 17:24
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Many Dell laptops come with 2 power supplies (bricks) one for just powering the laptop and another for powering the laptop while in a dock (and assorted accessories). Some docks have PCI slots and other doodads that require more power than the smaller brick can provide.

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The E6420 actually does run slower when connected to such a power supply. Believe it or not, I have 2 power supplies here. When I plug in the weak one, the desktop gets sluggish (e.g. scrolling in the browser). Once I plug in the more powerful power supply, the sluggishness is gone.

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This has nothing to do with the power supply and is more to do with the operating system power profiles. If you want to run at full performance with an underrated power supply then go to Control Panel -> Power and select High Performance. You will loose all of the power saving features that your CPU supports, meaning that it will kill your batter a lot faster but will no longer have any "sluggishness". –  Mokubai Jan 30 '12 at 20:30
    
@Mokubai You mean power supply, not battery. Correct? What do you mean underrated power supply? One which supplies less than minimum required by laptop? –  Boris_yo Jan 31 '12 at 1:50
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@Boris_yo I meant battery in that last sentence as high performance mode in the OS will drain the battery faster, though it will not damage the power supply or battery directly it will potentially drain the battery faster and more often causing it to die sooner. By under rated I mean less than is preferred by the laptop (as denoted by the BIOS warnings), it may well still be enough to power the laptop but it is not optimum. –  Mokubai Jan 31 '12 at 17:49
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