Darthutos :
as soon as someone upgrade a gpu or add a few fans/hdds he would need more wattage on his psu.
or do you want everyone to buy a new psu he/she buy a new gpu or gpu in sli mode?
Fans... seriously? They draw like 0.5A max (usually when they're spinning up... less once running. Unless you're putting together a HTPC with like an 80W power brick or something fans can just be bundled into the "extra stuff" column where you add your headroom.
And HDDs... even a power hungry drive like the WD Black rarely pulls an Amp.
I never advise anyone to get a cheap PSU, but people go completely overboard with wattage. Let's do the maths...
65W Locked CPU,
Even if, somehow, the Mobo, fans and HDD managed to draw 100W (which they won't by the way, they're unlikely to draw more than 50 under full load), that still leaves over 270W for the GPU before you're hitting the rated continuous wattage on the 12V rail for that CX450M PSU... and that's with all the other components drawing their max loads. That's a stupid amount for an RX 480.
A 450W PSU is safe and plenty for that build, and likely fine for future mid-range GPU upgrades, which tend to sit in the 120-200W range.
By all means grab a 550W if it helps you sleep better at night, no problems. But 650W really is overkill.
One of the experienced PSU experts here on the forums run folding at home (or some other GPU intensive workload, I can't remember) 24/7 powering 2 GTX 970s on a 520W Seasonic PSU. Now that's cutting it finer than I would advise, personally, but he measured the power load at the wall and it was well within spec for the PSU (maybe around 70-80% load), all works fine and has for a long time.
Another anecdote for you: an engineer told me a story once about a regional airport in Australia which has one of the thickest and strongest runways in the world. The plans had to go through something like 15 layers of bureaucracy, and no one was entirely sure just how thick a runway should be, so each person added 20% or so to the design, just to be safe. The end result, which was actually built, was so absurdly thick that this guy believed you could theoretically nose dive a massive aircraft into the runway without compromising its structural integrity... it was meant for light aircraft and small, regional passenger planes.
The same thing seems to happen when choosing a PSU. Of course let's advise good quality PSUs with some headroom, but let's not go overboard please!