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Differences between a 75 and 65 watt power supply? Answered

The problem is this: I found another laptop power supply rated at the same voltage but slightly different amperes and wattage.
19 V
3.42 A
65 Watts (guessing due to V x A = W)

19 V
3.95 A
75 Watts

I tested both and their voltage seems fine and nothing wrong with the older 75 watt power supply with two pongs. Will there be an issue with the wattage differences? And will the amperes be a problem if my laptop is rated for 19 V, 3.42 A?



Best Answer 7 years ago

The power supply rating tells you the maximum current which the supply can provide. Your device (in this case, a laptop) will pull as much current as it needs to operate (or charge the battery, or whatever). If you connect a supply with a lower rating, then that supply will overheat (too much current being requested). If you connect a supply with a higher rating, it'll be quite happy :-)

Well, I believe your information seems right after all. After a while of use (2-3 hours) nothing yet burst into flames. I'm guessing the laptop is simply drawing what it needs like everyone said. For now, the HP plug fits just like the Acer, with the minor problem of inner diameter.


Amperage or Wattage (excepting 'constant current' supplies, which are very specific and rare) put out a specific voltage, and can supply that voltage at up to the max amperage. Above that amperage, their safety systems shut them down, limit them, or worse, blow them up.

I kept my reply non-specific as to amps vs. watts. For DC, they're equivalent up to a scaling factor (duh :-), and the numerology depends on what's printed on the label. Most wall warts probably have some sort of internal fusible link, but certainly don't have proper replaceable fuses for overcurrent failures :-)

The good thing is that it recharges and the laptop acknowledges the power supply and switches to full power mode. The next problem is the plug and jack is getting warm, but not on the cable. Is this a sign? Or my method of using tin/aluminum foil to fit the wide diameter HP power supply is causing too much resistance?

You didn't mention introducing a high-resistance/possible-short into your system :-/ As Adam Savage has said numerous times, "Well, there's your problem."

Use it, it won't harm your laptop.

Also make sure that the replacement power supply has either a DC or AC output (the same as whatever the old one was) and that the polarity is also the same as the old one.