I've got a couple of old x64 Latitude D830s that I've upgraded to 8GB memory and dual SSDs, so I still use them for light-duty activities. They operate off of the 90W PA-10 power supply.
A few years back the 230 watt power supply in my M6500 died and I discovered that the 90W PA-10 would either charge the M6500 if it was turned off or keep it running if the battery was already charged. After that I carried the extra 90 watt PS when I knew I needed to run the M6500 during extended flights. Not exactly rocket surgery, but it worked.
Now I've got an HP ZBook 15 with 200 watt PS that I can operate similarly with a 90 W Slim AC adapter while flying. I'm not sure if they're pulling a full 90 watts on the plane though. I run all SSD and no DVD or USB drives. Even when running on the big power supplies they run a lot cooler than when first delivered from the manufacturer with HDD etc.