Are the "universal" laptop chargers safe / how do they work?

Question

I recently got a "Boltpower Car Jump Starter, Rocket Socket" that had an interesting feature, it had some odd looking adapters for laptops (none helpful for me unfortunately), that are supposed to charge a laptop battery.

The odd thing about this adapter is that it has a button that easily toggles 12v, 16v, 19v, off... as I understand, laptops need input power at the specified voltage and minimum amperage (in my case 19.5v 4.6a). I have to wonder if this is actually safe as laptop power... and if I found an extra plug and wired it to it, would it be safe to plug in?

The description on Amazon says "over current protection, short circuit protection, overload protection, over-voltage protection" and I'm curious what method they use for this - is it easy to implement if I were to build a custom charging adapter or kinetic generator of some sort - or is this expected to be protected on the laptop battery, similar to the overcharge protection that's part of every device with a li-ion?

Answer 1

It is hard to comment on the quality of all "Universal" chargers, but they basically are selectable voltage SMPS which can be quite useful beyond just charging laptops which use another SMPS inside to regulated the charge of battery modes (CC , CV and off) and then another SMPS inside to regulate all the CV's required for all devices and MOBO.

They come in a wide range from 65W to 150W.

They are not designed to charge any batteries directly.

All the "Universal" types I have tried use remote voltage sensing at the plug with extra wires so that cable losses is nulled out.

I have used mine for dimmer control on 50W of LEDs with good results by figuring out the voltage bias control pin, Vref pin and ground.