What kind of power connector is this? Attached to Adafruit 32x64 Matrix
You will need to make an accurate measurement of your connector to decide if it's one of the following.



VH-396

Could it possibly be a VH-396 from JST?

Pitch of these is 3.96mm, ie 0.156-in.
http://www.jst-mfg.com/product/detail_e.php?series=262


A=(npins-1)*3.96mm



KK-254

The picture at Adafruit (of one of its 64x32 displays) looks like the cable has a KK 254.  These are common as power connectors for floppy disks and some older small hard drives.  But the pitch is too small, 2.54mm.



https://www.molex.com/molex/products/part-detail/crimp_housings/0022013047



It also looks like Molex SPOX connector, which comes in 3.96mm and 5.08 mm.  

Product family page: https://www.molex.com/molex/products/family/spox

There are good dimensional drawings in there, here's a portion:

SPOX 3.96 mm (0.156-in), also known as KK-396.


Hole is given as 1.8mm, pin therefore approx 1.27 mm square pin.



SPOX 5.08 mm (0.2-in)


Hole is given as 1.8mm, pin therefore approx 1.27 mm square pin.