@danderson personally, I prefer to go with either 48V, 20V, 12V or 5V in DC application depending on what's convenient.
The 7,9x5,5mm ThinkPad barrel jack can do up to 11,5A originally, giving you 230W at the plug end.
- Pretty shure they did standardize it for 16A given all classic thinkPads used it except the very old ones.
That being said #USB-C-#PowerDelivery rocks and there are off-the-shelf ICs and boards to negotiate a ceetain voltage/amperage for any needs.
- Second best is #PoE++ 802.3bt Type 4 which is ~ 60V and gets you 100W and at least 87W at the device end.