I am downgrading my Supermicro box and I want to get a 400w~ PSU, but I don't know if it will work. Anyone know their way around Supermicro? The chassis is a SuperChassis 826BA-R1K28WB that comes with dual 1200w PSU's. When my load is less than 100w most of the time, I am losing a lot of efficiency
I personally wouldn't worry about it enough to warrant buying different PSUs. Even if efficiency drops 7% at say 80W, you're looking at less than $5 a year in electricity extra (at $0.10/kwh) if this is running 24/7. It will be difficult to recoup the cost. If you insist however, you'd want a pair of PWS-501P-1R.
While I second the 501P's (have a bunch and love 'em), you also can convert the box to single psu (non hot-swappable) to get lower power psu's going (mostly gold level though). Not sure what the matching part number is but I could find out if you are interested, got a couple of 825's which have fixed single PSU's