can you use a psu that doesn't support haswell on a haswell or skylake build?
??? a psu is a psu as long as its not some propietary garbage or $5 direct from china
Yes you can. The only difference is that the PSU will not support C6 and C7 low power draw of the Haswell/Skylake Power Supply which means that at Idle there will be a few more watts drawing.
I just learned something new. Thanks for the knowledge bomb!!!