You won't find a decent reliable 400w PSU for that case.
http://www.ebay.com/itm/New-Genuine-Dell-Optiplex-760-780-SFF-Power-Supply-235W-PW116-R224M-H235P-00-/222258829825?hash=item33bfa89a01:g:UnsAAOSwLnBX5He0
That system has a proprietary power supply , there are no real upgrades for it..It's 235w.
Hey, again I don't wanna waste my $300 system so, I'm wondering, Will this work?
https://www.amazon.com/Replace-Replacement-5188-7520-51...
or this?
https://www.amazon.com/gp/product/B00LPTY2HM/ref=ox_sc_...
Anyways, my (load wattage usage) is 266 W
My recommended PSU wattage is 316 W
Will any of those PSUs work? Thanks