5V Trinket only outputting 3.3V? Unless my multimeter is on the fritz, it would seem my 5V Adafruit Trinket is only outputting 3.3V when connected w/ DC power.

When connected via USB, totally fun. Full 5V. But if I disconnect that and connect a 9V wall adapter, the output of the 5V pinout is just giving me 3.3V.

Is that even possible?

I noticed the issue b/c my program wasn't running properly when connected via the DC adapter (but ran just fine via USB). So I tested the voltage and sure enough, 3.3V all around at basically every +/- connection.

Any ideas?
Unfortunately I do not have the ability to comment. What I can suggest is to look at the small 5 pin regulator and look at its markings. If the IC is marked with "QT33" then adafruit has stupidly soldered the wrong chip onto your trinket board. If it says "QT50" then the regulator is not at fault.