From Tripp Lite
http://www.tripplite.com/en/reseller-center/learning/reseller-faq.cfmn (see under section: What are Tripp Lite's UPS connection and equipment connection warnings?)
Tripp Lite recommends connecting a UPS system directly to a properly grounded AC power outlet. Do not plug the UPS into itself; this will damage the UPS. Do not modify the UPS plug, and do not use an adapter that would eliminate the ground connection. Do not use extension cords to connect the UPS to an AC outlet.
The warranty will be void if anything other than a Tripp Lite surge suppressors is used to connect the UPS to an outlet. If the UPS receives power from a motor-powered AC generator, the generator must provide clean, filtered, computer-grade output. Do not use Tripp Lite UPS Systems for life-support applications in which a malfunction or failure of a Tripp Lite UPS System could cause failure or significantly alter the performance of a life-support device. Do not connect surge suppressors or extension cords to the output of the UPS. This may damage the UPS and will void the surge suppressor and UPS warranties.