On Thursday, July 26, 2012 11:12:57 PM UTC-7, Tom Del Rosso wrote:

When a mobo has bad caps the PSU shuts down, but what triggers it?
What does the PSU see from its point of view? Peak current spikes?

I don't know if the Power_Good signal from the PSU is just a power-on reset signal for the motherboard or if the mobo is designed to shut down if that signal goes false. OTOH the mobo doesn't drive the Power_Good signal; the only thing it does drive is the Power_On signal on the green wire.

Motherboards have several voltage regulators -- CPU, AGP or PCI-E, and memory, and I'm guessing they're designed to shut down the power in case of overload because it could be too dangerous not to (tons of amps for creating arcs and fires); I can't say for sure because I haven't looked for this protection on many mobos, but my ancient PC-2007 had a "U" shaped bar to sense CPU current.

I don't know if PSU caps are damaged by bad caps on the mobo, but I doubt it's due to voltage but only current, and some reviewers have seen PSU caps and other PSU components fail when loaded to the PSU's full rated power with a testing machine -- see JonnyGuru.com , HardOCP.com , HardwareSecrets.com, which disect what they review, failed or not.