Csflipfreakz, in the interests of science, I request that you try your old supply in the new case to see if it helps. If it does, you've found your answer. If doesn't, you should look at another solution. Please report back.
I personally don't believe in huge PS's being the solution to some basic problem. Any PS maker may accidently assemble some defective PSs, and I imagine that is the reason why changing PS's fixes problems in the cases where it does. Normal people just don't have the capability to check if there are millisecond glitches on the power rails, so how would they know. A millisecond is huge amount of time to a gigahertz CPU.
The specs on cheapo, oddball brand PSs are probably a pack of lies, and IAC the QC has to be non-existent to keep selling price down.
The question though is if the mobo re-regulation from the PS down to 1.5V can cope with what it is given. In theory, considerable variations in input should make no difference in output. The output voltages are generated by switching the currents in the inductors- those donut shapes with wire wrapped around them. Any voltage can be generated that way by changing the rate of change of current in the inductor. There is a regulator chip that senses the output voltage and, by using feedback, adjusts the rate so the voltage comes out right.
I don't know for sure which PS rail is used to generate the CPU voltage, or if it is just one, but generally people mention 12 V. 12V at 15A is 180 watts. At 80% efficiency, the onboard regulators can supply 144 watts to the CPU. Seems like plenty for a 67 watt max CPU. True, a hard drive may take 10 watts out of the 144, and a couple of fans maybe 5. If you overvolt 15% (from 1.4 to 1.61V) the power is multiplied by 1.32, for 89 W. You would expect an HONESTLY RATED, non-defective PS to do OK OCing. That's why I am skeptical about the requirement for a super-duper PS. If the 12V rail supplies 18A, that gives you another 29 watt cushion.
Admittedly, asking PS makers to rate their product honestly is asking a lot, considering they can sell it for more the higher they rate it.
I don't doubt that people have PS problems, though, just like they have problems with everything. And maybe there is some mysterious property of power supplies that I am unaware of, but until somebody explains it, I remain a skeptic.