Laptop Power Supplies- AMPS Confusion

I've got an old fujitsu Siemens AMLO pro v3515 notebook with a dead power adapter to use it. The power measurements of it is

Power Details

Output Power (Max): 65W Output Voltage: 20V

Output Current (Max): 3.25A

I have one or two power adapters (some different vendors with following specs) in my junk stuff, working ones which I am wondering if I can use with this notebook!

Input Range: 100-240V AC Output voltage: 19v Output Current :3.42A

I don't know much about voltage and current differences. Is it recommended for me to use the adapter with 19V-3.42A where the Fujitsu's original was 20v-3.25A?? When I connected it for a while it powered on normally and computer booted, but I unplugged it. I just want to make sure if it's a suitable one and it will not damage internal electronic peripherals of the notebook in the long run.

Support is thanked :)

As it's a laptop the battery provides the power (when not connected to the adaptor) and it is an 11V. The external power supply output will be regulated by the battery charging circuitry in the computer to charge the battery and provide 11V to the computer power rails. I'd have thought 19V would do that as well as the 20V. This site has a replacement charger with the following spec 19V 3.42A (65W) Laptop Charger for Fujitsu Siemens Amilo Pro V3515 . If it was mine I'd use it without a worry!

You want to match voltages. It probably won't be good for it to undervolt it for a long time. I don't think it will damage it though but I still wouldn't use an unmatched voltage for too long. Amps are fine though, if it were a 20v 3.42a you could run it as long as you want, the device will only pull what it needs. I think you just happened to stumble across a perfect storm of adapters and voltages that the 19v provides just enough for the 20v computer to boot.

As a laptop tech of 10+ years I wouldn't ever recommend it, but it would be up to you to continue to use it. Adapters are cheap though, personally I would order a new one and MAYBE USE the wrong one for a short time if I HAD to use the laptop in the meantime, but would avoid it if I could.

Let's calculate the difference between supplies to see how much power they both deliver:

The formula for power is: Power (Watts) = Current (Amperes) * Voltage (Volts) or P = I * V

Original power supply: P = 3.25 A * 20 V = 65 W (as indicated)

The new power supply: P = 3.42 A * 19 V = 64.98 W (with significant digits this rounds to 65 W)

So both power supplies deliver the same power.

The issue is around whether there is enough voltage delivered or too much current delivered. Each electrical component in the computer needs a certain voltage. When you add these all up, your total voltage should be less than the voltage delivered by the power supply. In your case you're providing the laptop with less voltage than it used to receive from its old adapter (and more current).

When the engineer originally designed this laptop they would have selected a power supply that provided more voltage than the laptop needed to provide some tolerance and depending on how easy they wanted to make it for the consumer to modify or expand the devices in the laptop, they may have selected a power supply that delivers even more voltage than the stock laptop needs (this is common with desktop power supplies).

The question you have to ask is how much tolerance was built into this solution -- can you get away with providing 1 volt less (keep in mind at this scale we're talking about a 5% difference which can be significant)? Maybe. Maybe not. I don't know and I can't tell you. The engineer could have selected a power supply that delivers exactly the voltage needed. You won't know for sure unless you can measure it.

Depending on the laptop model you have you can likely pick up a replacement power supply. And here's the kicker, you'll find that the replacement may be a different part and in some cases it is also shared with other models from the same manufacturer. It is possible that it provides different voltage and amperes than your original (I have seen this several times with Dell). In this case the manufacturer knows the device and the power it needs and can make the decision as to whether the power supply is suitable for your model. It might be worth looking into what the replacement supply's specs are and seeing how they compare to your "junk" adapter.