I let out the magical smoke on a buck converter today

[pcprogrammer]

That sounds like a big one, like what I just ordered today 

https://nl.aliexpress.com/item/1005006365806926.html

I bought it for less via the choice page, you know, order at least three items and get free shipping. Payed only 2,69 for it.

When it arrives I will check everything before powering it up 

Very sceptical about its ratings - 20--50W perhaps, not 300!

I will find out when it arrives. 

[Silver_Is_Money]

It could have been an aluminum polymer capacitor, but either way it should not have exploded unless the voltage rating was too low, or the polarity was backwards.

It looked very much like these:  https://www.mouser.com/c/?marcom=113882612

[Silver_Is_Money]

Follow up and closure.  My new and more robustly built buck converter has  arrived, and it is working admirably.

[pcprogrammer]

 

Mine came yesterday and it works, but I have not fully tested it yet. Can't make out which MOSFET's they used without disassembling, so careful performance testing is needed to see if it can handle the 300W stated on aliexpress.