Thank you for the links, Turtle. I might give those a try.
I forgot to mention I once (about a year ago) got a double-port iOS charger, of the Macally brand. It expressly stated on the package it was suitable both for iPads and iPhones. Well, it likely wasn't ready for the demands of iPad 3... because it refused to charge the iPad and the iPhone simultaneously... and after about a week, it stopped charging completely. So I returned it to the store, and got another one. The same story happened again. So I also returned the second one to the store and resigned myself to the fact I'll just continue using 3 separate chargers for iPad 1, iPad 3 and iPhone 4. Well, I can live with that.
I use the two iPad chargers interchangeably, and they also charge the iPhone. The only thing that doesn't work is trying to charge the iPad 3 with the iPhone charger (iPad 1 works fine with it).