As you know, Pi 3B has a USB power inlet. I use
Canakit 2.5A wall wart, and never had any power problems. I chose that one because it had high current rating 2.5A.
You can convert the DIN to barrel plug by cutting off the DIN plug, measuring the voltage on the conductors inside the cable to find your 5+ and GRD, solder those directly to
Switchcraft 760, standard 5.5x2.5mm barrel plug. It fits Switchcraft 712 if you need a female. Rated 12V/5A.
Here's a 5 pin DIN female socket for adapting the Elpac's stock DIN plug:
DIN 5 pin female socket. You can probe the PS output plug to find the 5+ and GRD pins, but don't short the pins when probing!
Hold the ground probe to the shell with your thumb while you use both hands to steady the plug and the other probe.
Double check your voltage on the barrel plug before you connect it to Pi, I think wrong voltage will damage it, iirc