Delayed boot

I have two ReadyNAS 6 drive NAS- (ReadyNAS Pro Pioneer) - about 6 years old. They have OEM version of a Seasonic PSU - model SS-300SFD 300W SFX12V.

The problem that has happened to both NAS - after pushing the power button it takes about 5 minutes to power up. Another symptom is when powering down - either with the power button or the recommended way via web interface, they shut down then immediately powers back up.

This is a common problem for this model (Google readynas + SS-300SFD). The solution is to buy a new Seasonic 300SFD, which I'm about to do.

I've been building my own PC's for myself and other for years and I've seen about every PSU problem imaginable except for this one. The most dramatic - a Sparkle PSU that sounded like a rifle shot after pushing the power button. There was smoke but the MB and components were surprisingly OK.

My question - has anyone observed this type of PSU failure - delayed booting? The NAS is just an old Core2duo with non-ecc memory and I think Debian 4.0. Both units take about the same time to boot - 5 minutes. After pressing the power button there is some intermittent flickering of the NIC light on the back before the five minutes are up. I have both NAS on UPS and keep them on 24x7. I only noticed after I had to power them off and wouldn't power on.

Delayed boot