You want to use the properly sized PSU for your application plus some headroom depending on future growth plans.
You dont want to put a 1000 watt PSU in a system that only needs 500 watts. You may see better efficiency using a smaller PSU.
Read this: https://en.wikipedia.org/wiki/80_Plus
I always use various load calculators then add 10-20% on top of what I may use in the future in regards to SLI/Crossfire. Gives plenty of room to add second GPU plus watercooling, fans, etc.
In terms of PSU manufacturers.
Seasonic (OEM for many brands)
Superflower(OEM for many brands)
These will often be self labeled and found in other "Brands" as well, such as Corsair and XFX.
Always check who actually makes the PSU and not just the name on the side and look for a review on the actual PSU you intend to purchase as it may have more ripple or lower efficiency then another PSU of the same or less price.