Add a usb port anywhere.Surprised I couldn't find an stl available.
A little electronics knowledge is needed to find where and how to tap the DC voltage to power the usb port.
ALWAYS unplug before anything.

I'm not going to detail every step involved as I'm sure your requirements are not going to be identical to mine.
If you don't get it ...maybe you shouldn't be doing it.You CAN get hurt,burn your house down.....

Included is a marking template for the mounting holes.

The pictures detail an old 2.1 PC speaker system and Android phone,with a bad battery,repurposed to an internet radio/DLNA audio receiver that now,only needs one plug in my power strip.

CR-7

Doesn't Matter

No

.3mm

20% any

The usb cutout should be pretty tight to avoid the glue from seeping out.
It will probably need some finishing to fit the face of the connector properly

Simple FreeCad design

Tape around the connector or the hot glue will ooze inside the connector.
Fit the connector flush with the front of the panel.
Fill the space around the connector with hot glue.
Find yourself points on the board to supply power to the dc-dc regulator or wire an old 5 volt adapter to the mains voltage and wire the 5 volt output directly to the female usb.
ALWAYS unplug before anything.Make sure all mains connections are well insulated.
Adjust the regulator pot for 5 volts,I always try to stay around 5.1 volts.I actually have a couple devices that will not charge below that.

If your SURE the device can supply 2A more,the center two pins can be shorted together to trigger high speed charging.
I probably should add a separate fuse.

If you don't get it ...maybe you shouldn't be doing it.You CAN get hurt,burn your house down.....

LASTLY....DON'T BLAME ME,I'M JUST PUTTIN IT OUT THERE.