I thought Silverstone reputated with high quality PSU, May I know ur rig spec and any OC setting & possible details about the power source connect from PSU to wall plug scoket (do u use extension and share to multiple devices on that extension), I realised OC did increase my PSU temperature up to 45 °C after running 48 hours PSU fan do auto increase fan speed to make it maintain under 45 °C, I get the reading from  thermistor paste on PSU case part where near 24pin cable, and w/o OC is <45 °C, 38 - 40  °C, I never close the side case panel which I am sure the air flow inside is good enough (imagine 100 CFM ram cooler blow the hot air out set to 40 cfm also enough to blow out the hot air, inside the air-cond room ), even read from here or here which proof the 45 °C is normal operating temperature.
Just to want make sure is that every hx620 users have the same temperature reading with / without oc the CPU.

Even if u run 2 years 24/7 non-stop -> 365*2*24 = 17, 520 hours, u shd read about the MTBF of silverstone zeus 750w is 100,000 hours at 25 °C, full load. Urs only utilise 17.52% of Meant Time Between Failures than screw up already, what a poor quality silverstone somemore is zeus version  , u shd not share the PSU power with extension somemore up to 5 source socket connect to others, it may cause insufficient power "pump" to ur PSU, and cause current fluctuation (even with APFC, it only help reduce the voltage if too high, never possible generate extra voltage if power source voltage too low), and kill PSU life span, shd be make independant power source to PSU.

But from ur spec, it shd be able to run even with 450w PSU, why that silverstone dead still abit curious  , what 5 devices connect to the extension that share the power source with that PSU?

I dunno much about acbel M8, it is modular PSU anyway, and cooler master using acbel PSU and rebrand it, so far I know the greatest PSU is seasonic  , next to CWT.