65w vs 90w Laptop Power Supply Benchmark

I got a Dell Latitude D830 notebook a few weeks ago and it’s great. One thing I noticed, and it’s not a surprise; it doesn’t like the extra power adapter that I bought 6 years ago (3 Dell laptops ago).

The last generation of Dell power supplies are 65 watts, while the current generation power supplies output 90 watts. When you use a 65w supply on a 90w machine, you get a disappointing Windows alert:

65W AC Power Adapter has been determined. Your system will operate slower and the battery may take more time to charge. Please connect a Dell 90W AC adapter or higher for best system operation.

I wondered just how much impact this would have on system performance, so I got some free benchmark software (CPU Free BenchMark 2). This software clocks the time it takes your CPU to perform a series of registry, floating-point and integer tests. The lower the time, the faster the CPU. I ran these tests a number of times with various power configurations and here are the average results of those tests.

Dell Latitude D830 CPU Mark Chart

As you can see, using your Latitude D830 battery or 90w power supply are virtually the same. Using a previous generation 65w power supply provides only enough power for roughly 20% of maximum performance. It’s fine in a jam, but if you’re a two power supply user then it’s worth your money to get a second 90w power supply. I found one new for $10 (+ $13 shipping) at an eBay retailer.

UPDATE: Jan 12, 2009 – The $13 power supply I bought on eBay died after just 3 months use. It was potentially a counterfeit “OEM” power supply. It was very similar to the power supply that shipped with my computer, including high quality forming, metallic labels and high gauge cabling (atypical for counterfeits)… the only major difference was the weight. I’ve ordered another for $35, from another retailer who guarantees it is authentic. I’ll keep you posted.

UPDATE: Mar 11, 2009 – Some people have asked for some perspective on the 119 second time that I scored while using the 65 watt power supply. The slowest computer I was easily able to test for comparison is a Pentium 4 machine and it scored 38.85 seconds.

So, because the Core 2 Duo (2.5GHz/4GB RAM/Vista) took 24.83 seconds and the 4 year old Pentium 4 (3.4GHz/2GB RAM/WinXP) took 38.85 seconds, then 119 seconds is dreadfully slow. By my estimate, using a 65 watt power supply is like putting an 8 year old CPU in your machine. If somebody has a Pentium 3 up and running, it would be nice to find out the CPU Free Benchmark 2.2 score for that to know for sure.

6 thoughts on “65w vs 90w Laptop Power Supply Benchmark

  1. There must be a way to turn this off – surely the machine should be able to offer better performance with a 65w PS than with the battery alone.

  2. @anon
    I would have thought so, but that’s why I wanted to run these benchmarks. If the battery can output more than the 65w power supply then maybe the answer is no, the 65w power supply is not enough power for full performance.

  3. Went on holiday with my D830 and a 65W PSU. H264 video from my video cameara would not play no matter what. Yesterday had the same issue while trying to play MKVs with VLC – choppy and all.

    Using a 90W PSU fixed everything.

  4. I can confirm that. I didn’t do a benchmark, but my Dell E6420 with 65W power supply is awfully slow (sluggish desktop). Connecting a proper power supply immediately brings performance back to normal.

    Bottom line: don’t use a 65W power supply if your Dell computer needs a 90W one. You are massively losing performance.

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