80+ Gold certification doesn't essentially mean that you're buying into a good PSU. Might want to mention where you're located, what sites you have access to and what your budget for a PSU is? We could help narrow down a PSU to replace the 450W unit.
Just for the sake of relevance, no I'm not angry, it's just sad to see people flushing money down the drain while others don't have funds to flush down.
To add, Outervision and all the other wattage calculators are on the same platform, so they aren't saying anything different. For most builds I just add 100W to the power supply suggested on a GPU's box/support site and call it a day(after making sure that the PSU is reliably built). PSU's are made out of capacitors and if you study the graph's you'll see that they mention the temperature at which the unit is operating while showing the power output from the PSU, the wattage calculator does not factor in regions that experience unusually hot, humid weather all year round, meaning they degrade faster as opposed to a unit run in a region where they see nothing but cold.
Out of curiosity, did you actually open the side panel to see what your PSU's make and model is? If you didn't, how did you come to the conclusion that the PSU is 450W?