One supermicro enclosure comes with "3 SP382-TS 380W Power Modules for a total of 760W".
2x380W = 760W, okay, but there are 3! So where is the missing third 380W equalling to 1140W?? Is it hot-sparing, kicking in when one dies?
- What wattage is supplied at any given time, 380W, 760W?
- Or are all running at-once, with one having the ability to die leaving the server with 760W? (Is that wasting power, given that PSUs perform best at ~70 load?)
- Or is one waiting for action?
Best Answer
The concept is called n+1 redundancy. The reason three PSUs are commonly used is that it is more efficient to have three 380 W PSUs operating at 50% load and 90% efficiency than have two 760W PSUs at 37,5% load and less than 85% efficiency.
All that said you should consider that the PSU rating is for rough orientation only. For one thing, your system power consumption will typically be way below the peak rating. For the other, the value is usually just a sum of all available power bus ratings (there are plenty in a PC) and thus not useful as such for any kind of precise calculation.