AT&T claims the reason their router, the BGW320-500 sometimes factory resets itself is because it’s designed to do this in response to unexpected power loss, and if the house didn’t lose power, the power strip / surge protector may be at fault.
Which I don’t doubt might be the case, I have old, cheap, generic power strip.
So recommend me a power / strip protector you trust with your uptime. While I don’t need a UPS, I wouldn’t mind /some/ battery backup to smooth over brief power issues.
I use a tplink eap773, before that I used an old Asus router in AP mode until it died.