Were did you buy it.How long ago.How much did it cost.Do you really think we are interested in that.
really/necessary need to say what I need to power up but nvm some people are curious.
Yes you do. Or at least tell us what it draws.
But in this case I think the easiest way (and good and cheap) is to buy a new (laptop) PSU (eBay.
Why people on this forum are so curious stubborn?
The voltage of the PSU you have will probably drop to 19V under load. But yeay, even that's to high if it can only handle up to 18V.
I need to power up a imax B6 80W (11v~18v), I got a 20~22V 4.7A power supply.
10 silicon rectifier diodes in series, each rated at least 5A, will do this. [NB - At Least.](If you aren't going to need that "4.8A", diodes rated for less current will suffice.)Are you going to do this or is this just so much MM?
There is a standard circuit for dropping some non-trivial number of volts using a zener and a power transistor: