One thing I always recommend to people in the market for a PSU: DO. NOT. SKIMP. The PSU is the literal heart of your machine. Without it, nothing works, and if you get a bad one, it can kill your machine (and possibly fry the components). I recommend using one that is at least 80+ Bronze certified, and preferably 80+ Gold or higher. As far as brands go, I recommend Corsair and Seasonic for all wattage ranges, and EVGA and Antec for the 900W+ range. Pay the money for a good PSU. You will be money ahead in the long run.
I've done a lot of looking into PSU's. If you really want the best, I recommend this sony APS-112 from the early 2000's. It has busbars internally to handle the current, as well as a number of excellent design choices for extreme reliability. It is rated for almost 100A on the 3.3V rail and about 75A on the 5V rail. Each of those is stabilized by 40 thousand microfarads of capacitance. I could go on, but it's a real marvel.
Now while I agree that not skimping out on the PSU is a good idea, Having a 900W PSU for a system that draws 400W at most is absolutely wasteful. Those beefier PSUs are designed to run at about 70% of their rated load. If your build draws 400W, then get a 500W PSU and call it good.
As far as 80+, I recommend it. A more efficient PSU will save you money in electric bills, but the real reason is that since it's wasting less power as heat, it'll run cooler and last longer. There are a lot of very good reasons to get an "expensive" PSU at a lower wattage (like a seasonic, mentioned above). I also recommend reading teardowns and reviews.
Johnnyguru is a good place.
Here's a good example review that hits all the points I would expect. Full teardown, performance metrics running normally, and in a hotbox. You can see the quality, even if you don't fully understand what all the different components actually do. Is it worth the price? possibly. But it's easy to see just WHY it costs more than, say
this exampleIf you are interested in learning more about electrical theory and PSU design, I recommend their forums which have decent FAQs.
here is an example.
One reason you may want to get a higher wattage PSU is so you can reuse it in your next build. If you plan to upgrade, you can usually keep the storage, case, PSU, RAM, and sometimes the CPU cooler the same while just upgrading the MB, CPU and likely GPU. A good PSU will last many years for many builds.