Reasons for replacing a SMPS include opting for what is called 80+ certification, which is simply increased efficiency, and they are rated from bronze to silver to gold to platinum. Efficiency is, simply put, how much electricity is still available after the unit converts 110 Volts of ALTERNATING Current (or 220 VAC for that matter) into a flat line DIRECT Current (there are a few different voltages that they all produce such as 3.3, 5, and 12 VDC primarily). Because all electronics turns SOME electricity into heat and such a 50% efficient 500 watt power supply would effectivly only supply 250 watts of usable electricity. Of course, things get slightly more complicated with electicity, but that is very close to literally the difference.
Here is a breakdown of the different versions: »en.wikipedia.org/wiki/80_Plus
But it can take up to months for the difference in efficiency to pan out on an electrical bill. However, with greater efficiency comes cooler running, so your air conditioning sees a lighter load too.
Other things that people look for in a new unit:
Low Ripple/electrical noise (when converting AC to DC, how good is the filtering circuitry such that less unwanted signal comes through. Low Ripple means longer lasting motherboards and drives. It can be very important, but sadly, too few people know about this issue and fewer shop based on it for an issue. Suffice it to say, review sites are your friend, meaning google is your best pal.
DC voltage stability and reduced load to voltage drop delta. As you load down a unit, the supplied DC voltage changes, it drops lower. Good units suffer this much less because they have better regulation circuitry.
Better cooling (heatsinks, fans, airflow design).
Now: your current unit is a really good unit. I wouldn't replace it right offhand unless you were opting for equal quality and better design/features as described above.--
Join Teams Helix and Discovery. Rest in Peace, Leonard David Smith, my best friend, you are missed badly! Rest in peace, Pop, glad our last years were good. Please pray for Colin, he has ependymoma, a brain cancer, donate to a children's Hospital.