trying to power 5v device

Hello all. Before I explain, I would like to tell you that I am at the very beginning stages of being a a beginner. So thank you for your patience I am trying to power a wireless hdmi transmitter via 12v battery source. i created a connection between the battery and a usb male cigarette adapter (it was previously used to charge my cellphone in the car) I am using the usb male cigarette adapter to convert to 5v. I created a cable that plugs into the USB and into my wireless device. My problem lies in the fact that even though the 12v source is effectively now giving me 5v, my device will not work. The LED light comes on but it will not transmit or receive HDMI signals. I am quite perplexed. I am wondering if my solution is providing unregulated power as opposed to regulated. Any ideas? Thanks Everyone!!

It is possible that the adapter does not supply enough current. Even though the 5V is correct, there must be enough current available for the specific device. Look at the specifications on the HDMI device and see how much current (in amperes or milli-amperes) it requires. Then, see if the adapter has a current rating.

If you have a multimeter, which can be obtained very cheaply and is enormously useful, you can check the voltage being supplied to your transmitter while it is running. As tracecom has speculated, it might not be holding voltage when loaded.