My roommate got me an USB port equipped power outlet for charging phones and stuff, but where I needed it to be was in a double gang box in my workshop, so forget the face plate it came with. I had to modify the metal face plate already in place!
Step 1: Trace the Holes From the Provided Face Plate to the Existing Face Plate.
Put the face plate with the USB holes on top of the original face plate. I recommend using the mounting screw to attach them together, and putting your fingers in the outlet holes to keep the plates aligned while you trace with your other hand.
Step 2: Measure the Width of the Hole for Drill Bit Selection
Step 3: Punch Marks for Drilling.
I set the caliper to half of the hole's width and scribed a little + for punching. Since we're making a rectangular hole, make a punch mark near both extremities.
Step 4: Drilling
-Drill pilot holes with a small bit, otherwise the full size bit will wander out of the punch mark.
-Don't forget to slow down your drill for the bigger bit! Also, sharp drill bits and some oil greatly improve the experience.
-With the pilot holes, it's easy to align the bigger drill bit.
-The drill holes being the width of the USB port, what's left is to bridge the gap between them!
Step 5: Bridging the Gap.
I have this dremmel bit that looks like an end mill. I chucked that in my press drill to mill out the metal between the two holes.
Step 6: Deburr
Removing the burr on the outside was easy enough, but I had to use something else for the inside : A mildly worn utility knife blade.
Step 7: An Extra Step for My Particular Setup
I needed to break of those tabs otherwise the outlets don't fit in the metal cover. Your mileage may vary!
Step 8: Test Fit
It's important to check how well the slots fit over the USB ports of the outlet before putting everything back together. I had to touch up the milling a couple of times before the plug would fit through properly.
Step 9: Enjoy!
Well, not without putting everything back together beforehand...
The benefit of this setup is that now I don't have to bring my USB rechargeable bike lights to my computer for charging!