Considering you have the equipment plugged into an APC UPS, which will condition power as well as provide protection, I'm inclined to suspect a router issue and not necessarily a power issue.
Click on my name above in this response and read my “how-to” guide titled, “Troubleshooting Wireless Issues” and go through the steps listed there. Report back and we'll continue troubleshooting from there.
Oh, and one more thing, don't overload the UPS. Double check and ensure you haven't. If you have, remove a device or two.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.