I would like to share a bit of my disappointment with the PSU GP50A13A-R1B.
It is undeniably compact and all-in-one solution but let me tell you that it doesn't deliver.
I'm reading 4.6v (CPS1) to 5.05v (MV1B) and ok...most board play fine with such low voltage but not Killer Instinct which goes on boot loop or doesn't boot at all.
Any known/tested table top psu to recommend?
(Already made a shorter harness to ease the load and gained about .05v for the 5v rail)
The problem seems to be the +5V amperage output. Maybe 4A is not enough for the bigger boards. That, and the lack of pot to regulate the output may cause your problem. For reference, I use my supergun with a MeanWell RT-125A. So far, it has worked with CPS2, an MV2F, Atomiswave, PGM, CPS1, MK2 and MK3. Only drawback of it is that it does not power on unless you load it with more than 1A, so smaller boards that do not consume much (MV1B, MV1C) usually cannot be powered with it.
Regards.