I'm using this 30W RAVpower brick and 5v-12v usb cable and everything is great.
Here's the custom IO panel. I had the manufacturer add all the holes then I added my own for the nema connector and the lighted button I use with my powerblock hat. The HDMI port is connected to a manual 2-1 1-2 HDMI switch so I can easily do video out to my TV.
I had/have plans to add a mains switch possibly at some point, and that's why there's a label and spot for said switch. I may use that area to break-out the switch built into the HDMI switch box instead though, as that'd be more useful.
Here's the inside with the RAVpower charger and the 5v-12v usb cable. The box on the cable doesn't get any hotter than the charger so I'm assuming all is well. Everything, other than the pi, is held on by either double sided 3M adhesive pads, 3M dual lock or cable tie adhesive pads.
BTW that box under the RAVpower unit is a micro sd - standard sd extension. Makes getting your sd card out of the picade so much easier.
Also, I had to buy at least 3 metric nylon screw kits on amazon in order to get the parts needed to have that pibow case and powerblock securely mounted to the door.
I honestly had more fun building, modifying, and getting retropie setup than I've had playing the games. The games were just a good excuse to start the whole project.