Well about that Frontech Wireless headphones, it does come with a 3VDC input for the transmitter but they have not provided adaptor. I had an old adaptor but it did not work well with that but it worked fine when I used it on battery power so I guess the adaptor was faulty will check with a different adaptor.
and this is the product that I am talking about : http://www.frontechonline.com/3411.html

The FM radios works pretty well and even the wireless headphones are good and I could hear it across to another room. 2 independent bands for wireless and FM are really helpful. Would have been best if they had provided an adaptor for the transmitter. And the price Rs.589