only the highest tier, most expensive lines are warrantied 10-12 years: they use much higher grade capacitors they can rely on lasting that many years
I purchased my EVGA 650w GQ 210-GQ-0650-V1 for $80 many a year ago (although these days it is $115). Hardly a top of the line unit. At the time it came with a 10 year warranty.
I would argue midrange units like the above mentioned PSU can easily make its warranty period and more.
The OPs power supply is a superior model to mine, he is using a EVGA Supernova 750 G+, which came with a 10 year warranty, high quality Japanese capacitors, premium fan, upgraded electronics focused on <1% deviation on all rails, and 80 plus gold rating. His power supply will easily function with this load for years to come.
Odds are that his pre-pandemic PSU is superior to a PSU made during this pandemic.
Capacitors age regardless of electrical load, although heat is a factor in advancing the aging of capacitors.
These midrange units have proper ventilation and non-Chinese Caps, the aging is not that big of an issue.
You can use an older power supply and as long as there hasn't been a catastrophic capacitor or other component failure it may still deliver power, but the total power capability and hold up time will suffer.
These units were purchased from a reputable brand and are still under warranty. It is unreasonable to think they would not meet spec.
When you have heavy loads, transient spikes, etc. an older power supply commonly will start to show problems due to aging.
I loaded my midrange 650 watt unit down with a rx6900xt (350 watt peak), a rx Vega 56 (312 watt peak), a 4790k (130 watts peak), and it had no problems associated with aging. Yes, its OCP did trigger as designed in a correct and harmless manner. And yes, I pushed it over its spec over and over as I experimented with just how far I could push it. Nothing bad ever happened. It is mining Eth to this day.
It's become a common theme among the enthusiast community to not trust a power supply beyond it's given warranty since there is a strong correlation between capacitor/component quality, their longevity, and the given warranties.
I feel compelled to point out the OPs "old" power supply is still within its warranty period.
I would also argue the community is wrong here, a midrange unit from a reputable manufacturer will last years to come.