What connector type is this 3-pin connector from an HP printer power adapter?
OK, I contacted Molex and I found out that this is a Molex Mini Fit 3-pin connector custom-made part because the polarization is different from the standard Mini Fits. I asked which part number most closely resembled this one and was told Part Number: 39-01-4032, Mini-Fit Jr.™ Plug Housing, Single Row with Panel Mount Ears



I ordered some samples and this fits amazingly well. It has 2 square holes but they fit the mating 'pins' well. I had to cut in a groove to accomodate the key and I had to file down the lock tab so it could be disassembled without having to use a finger to lift the tab. So I have all the functionality of the original connector.




So it looks like alex.forencich and Michael Kjörling were right about the general type of connector. Thank you.