well, i don't like UPS. They are a waste of money, if you have decent psu i don't really think we need it.
My brother had reboot issue when power used to go out but after he got a good psu the problem went away
Huh? All that proved was the first PSU was faulty or a piece of junk.
i think quality PSUs have enough switch time charge to prevent power loss
Sadly, that is not true. The ATX Form Factor standard only requires ATX PSUs to "hold up" power for a mere 17ms when the mains input drops below 90VAC (or 180VAC for 230VAC mains). 17ms is much faster than humans can detects (in the flicker of lights, for example). And if you look at PSU reviews, many of the top quality PSUs don't even meet that requirement.
So while you are right, a quality PSU will (or should) "hold up" power during extremely short dips in voltages, those are only a small portion of the power anomalies typical supplies encounter.
But you missed or ignored the point - even though you quoted me! The point for having a good UPS with AVR is NOT about power loss, but about regulating the voltage to include suppressing surges and spikes (high-voltage anomalies), and compensating for dips, sags, and brownouts (low-voltage anomalies).
Also, when selecting an UPS, it should be sized to support not just the computer's PSU, but your monitor and all your network gear too.
I found running a UPS rather expensive with the need to replace batteries
The need to replace UPS batteries is certainly a downside. But so is the cost of replacing a computer. And I note for many, it is the data that is the most valuable, and perhaps the downtime too - especially if they have to replace the computer.
That said, never buy replacement batteries from the UPS maker unless you want to pay full retail over-priced
prices. Always shop around and you can easily fine deep discounts on Amazon or at one of many on-line battery sites for the exact same cells.
As for your super-capacitors - well, a typical UPS of decent capacity uses two 7Ah 12V cells. Many use 4 cells, some use 9Ah cells. I don't see how your 1Ah 12V capacitor array is going to be a suitable substitute to provide enough capacity under load. It might provide few scant minutes of run time, depending on the load but that is only useful if the user is sitting at the computer at the moment the power goes out so he or she can finish typing their sentence, save their document, close their open programs, "gracefully" shutdown Windows and properly power off the computer before the capacitor array runs out of charge. This is easily accomplished with batteries which can typically provide at least 20 minutes of runtime.
I personally don't see how spending $30 every 3 - 5 years on a pair of 12 7AH SLA cells
is going to break the bank. Considering that capacitor array still requires the user purchase a UPS for that capacitor array to go in. The new UPS will already come with batteries, and your very low capacity array costs $70. I don't see how that is saving money. You could buy two new set of batteries for that $70 - another 6 - 10 years on top of the original 3 - 5 years with the OEM batts.
A fun project, yes. But worth it? Ummm, no.
But all this is off topic. This thread is about leaving power strips on full time. And yes, that is fine.