My really old antec true power 550 lasted, i modded it soldering on a 4 pin mother board atx plug because this power supply is older than the pentium 4, and molex to pcie connectors. When i bought it someone said.. "You will never need a 36amp 12volt rail, that's insane." A few years later.. "36amps is barely enough." lol. This power supply was a champ, running crossfire HD-4870's back in the day, and 90nm cpus also sucked lots of power too.
It got sold with a used pc that had a hd-4870 in it. I had bought a new OCZ Fatal1ty 550 with two 25amp rails for a total of 50 amps that was on sale with a cool looking led light. I am still using it.
It's mostly the lifespan of parts like the fan, and caps in the cheaper power supplies. Also the budget ones rarely can put out what they claim or they resort to revving the fan to do it. Cheaper power supplies usually trade noise for power. So a corsair CX 600 will scream the fan when under load while my OCZ is still quiet. I had to oil the fan on the CX 600 and buy and replace a cap. It's in my dad's pc and doesn't even work hard with a A8-3870K using it's IGP.
The 500watt EVGA will work and even let you overclock, but someday the fan will need to be oiled or replaced, maybe a cap will be bulging or leaking. It will likely deliver the power it claims but rev the fan under load. I am just saying what my personal experience has been with cheap vs. quality.