Can I use a different laptop power supply, same tip polarity, voltage, at least same amperage

Question

My understanding is that new Lithium-Ion batteries can be dangerous because of some of the circutry surrounding them. To put it simply you do something wrong and they will start on fire or even explode. In that context, I have heard it said that connecting the wrong power supply is dangerous, there are sophisticated electronics controlling the charging/power based on battery charge and present power draw, and that power supplies will even stop drawing "wall poer" if the battery is charged and the laptop is off.

In olden days, if I had a power supply that supplied the same "tip polarity" ( also the same jack of course ), the same voltage, and at least the same amperage, everything was OK. Is that still the case, or do power supplies have to be paired with laptops?

Answer 1

In every piece of consumer electronics I'm aware of that uses lithium-ion batteries, from phones to laptops, the safety-critical charging circuitry is either part of the device, or actually integrated into the battery pack inside the device. The external power supply, then, is still fairly "dumb", as far as battery charging goes (it may have more sophisticated circuitry for efficiency's sake, but it essentially just provides current at a fixed voltage like its ancestors did).

One reason for this is that the (integrated) battery charging circuit probably has a temperature sensor embedded in the battery pack, and perhaps internal connections in between the cells in the battery, and it wouldn't make sense to run all those wires out to the external power brick.

I'm very hesitant to say that you can always swap power supplies around, because for all I know there are common devices for which that's unsafe, but in my own limited experience, I have only encountered laptops/tablets/phones which integrate the Li-ion charger into the device or battery, not into the power brick.

(Things which use a USB connector for charging may do some simple signaling to tell the device how much current it is allowed to draw, but that's a separate issue.)