I did a shoot yesterday with the Panasonic HPX 370. The camera worked fine with my AB Dionic batteries.
But It wouldn't work with either of my AB Tandem charger/power supplies. When I asked my friend who owns the camera about it he said they had the same result but hadn't had any time to look into the problem.

Any thoughts?

Thanks.

In the Battery Setup (#8 in the Main Menu), there are 2 options for Ext DC In Sel, AC Adaptor or Battery.
Perhaps your camera is set to Battery.
Ed

Thanks Ed,

After I had written the question I'd realized I should have mentioned that I tried that. Just to test it I tried the external setting and the "battery" setting as well since the Tandem unit fits to the back like a battery instead of going through the four pin. Also another piece of information is that they had tried it with another power supply that plugs into the four pin ac in on the back of the camera and it worked fine with that but not their Tandem unit.

I was fine for my shoot since I got about four hours out of a battery and I had three and the chargers with me. I'm mostly wondering since I may pick up one of the 370's myself and it'd be nice to have it work with my power supplies and the batteries that I already own.

Good luck. I use IDX (and I use a non-mountable IDX charger/power supply), so that's about as far as I can go with ideas.
Ed

I had the same problem with the Anton Bauer tandem charger/power supply. When I put the tandem unit on the back of the camera, I cannot get the camera to power up.

The same AB tandem unit powers up my JVC camera with no problem. Not sure why it doesn't work on the Panasonic HPX370.

If Panasonic or anyone else has any insight, please share. Thanks!

Here's an answer Ralph got on another forum:

"You mean you're attaching just the tandem charger without the battery attached to it?
Put the battery on, go to menu option "Battery Setup" and set the first option "EXT DC IN SEL" to "battery", now it will work with just the charger on. "