rndp6000 won't boot or reset

Did you test the voltages under load?  If not, the test is far from comprehensive.  While there are two 12V load segments, they tend to be tied together at some point (though I have not tested that with the ReadyNAS supply).  Your next best step is to try another supply.  Rather than buying one that will fit internally, you can use a standard ATX supply (that perhaps you "borrow" from a PC) and plug it in externally.  If that doesn't fix it, then it's something else.  Without schematics, which Nethgear has never made available, further troubleshooting is mostly shots in the dark.