2 19VDC laptop chargers in series

[DonRotolo]

Ether, it can't hurt to ohm out the output wires to the input wires. Anything other than several kOhms or more means 'come back and let us know so we can figure this out for you'.

I assume these are switching supplies, and these run at several dozens of kHz, thus using a tiny high-frequency transformer, which provides isolation. I suppose one could build one with a shunting configuration, but there are common mode issues (noise) that often nixes that idea.