The plug on the first one is a bit shaky because I had to resolder it multiple times until I found that there was a hidden second ground cable from the battery-contacts to the flash head.
So I was wondering why it would charge and everything but not flash when switching from the battery contacts to external power and thus accidentally having the flash head itself float without ground.
I'm using a 6V 2.25mAh wall wart style universal power supply with overload protection.
Others have used 1.4A and 2.8A and it seems that you can go way higher then 2.8A to get even faster recycle times.
I am not sure I want to go there as I find this more then fast enough and don't want to overheat my flash head.