Possible? Bhai i am certain its because of UPS. Whenever some asked me if its OK to charge on UPS/Generators, i forbid them to do so. Then come out some stupid people who genuinely think its OK just because they have never experienced it ... because of their luck. (Unless you are using a Sinewave UPS, in which case its alarming if it blew up your charger)
Anyway, Its highly unlikely you are going to find the original charger for it so save the hardwork of finding one. Keep using the iPad charger. Nexus 7 charger is also slow and takes upto 7-8 hours to fully charge it. If it takes the same with iPad Charger, its OKAY.
Alternatively, you can opt for a Original Samsung charger as well, or ANY charger which meets the following:
Original Nexus 7 Charger is rated @ 100V-240V @ 0.3A ... i have the USA version.