With OPs initial configuration there was no problem at all. only some people claimed that 360W wasn't enough for such a tiny system.
Who claimed that? It wasn't me. I merely said that it was cutting it close and suggested the 450W. It's a smarter choice. And I showed my reasoning.
btw, the FreeNAS Mini uses a 250W PSU for 4 HDDs and the same mobo.
And the AsRock Rack 1U12LW-C2750 also has a 250W PSU for 12 HDD's and that same mobo.
I'm sure that means it is perfectly fine to just go and trust that it will work out and not fry your drives. No, but seriously, just because someone designs something, doesn't mean it is engineered well. This whole discussion is about properly engineering things. The FreeNAS Mini is a poster child example of everything wrong with PCland. It's a product for a company that's trying to produce something that balances functionality with not being totally priced unreasonably out of the marketplace compared to similar units from other NAS vendors. That doesn't mean it is well engineered.
If you don't give a flying f about proper engineering, the original poster would be just fine putting a 150W power supply in there and just hoping that there's enough margin in the supply to handle the occasional spikes from drives starting up. I'd give it 90% odds on appearing to work just fine. But I'd also give it great odds that it'll cause damage to the drives eventually, and that the power supply will catastrophically fail by the time it hits five years.
It's the difference between "that's good enough to be likely to make it through the 1 year warranty period without a statistically unacceptable number of failures" and "this is engineered well enough that it'll probably still be just fine and dandy in 10 years."
We encourage people to buy ECC because we care about the integrity of their data and because we believe that they want to be able to reliably store data for the long term. Why would you cut corners on something as trivial as a power supply? It's a foolish thing to save ten bucks getting a smaller supply when your entire system's health is dependent on the proper operation of the supply.