Since I'm nerding out tonight, I did some tests to verify voltage drop. Not the end-all super scientific test, but I think good enough.
I soldered on some test pins on a PCB to simulate a game, and loaded it with 5 amps on my fancy electronic load - this is as much as you're ever likely to encounter I think.
https://wiki.arcadeotaku.com/w/PCB_Power_Consumption
The higher the amp, the more voltage drop you will have given other things being equal.
Here is the measurements on the input of the Jammafier:
And here I switched the probes to the 'game':
Some rounding and not taking absolute accuracy of the meter into account:
Reading at Jammafier power entry: 4.96V
Reading at game: 4.91V
Voltage drop: 0.05V when loaded at 5A.
Ran the same test setup with the Namco one and it voltage drop was 0.23V - I was expecting it to be a bit higher.
The production run of the Jammafier will use a jamma edge connector from a different manufacturer - but I don't expect numbers to change much or if at all.
For final test, and the one that is probably more relevant to 'normal scenarios' - I tested the Jammafier with 1.5A load:
Reading at Jammafier power entry: 5.2914V
Reading at game: 5.2880V
Voltage drop: 0.0034V when loaded at 1.5A. This is so low that the accuracy of meter and probes probably come into play.
Executive summary: it werks well