I do not really know where to post this so hope I have posted it in the right place, today I have bought one of these MiTec Micro USB to HDMI cable's/gadget and despite trying have not been able to get the display from any phone or tablet on the tv.

It has a Micro USB cable coming out of it which I presume should be connected to the phone or tablet and the other end is where the HDMI cable plugs in, at the side it has another slot which I presume is to charge your phone or tablet but having said that I have seen a demonstration of a similar device on Youtube and the device that is demonstrated needs a power cable plugged in at the side.

Surely a device would not be sold which then required you to get a power cable as an extra before you can use it would it?.

I hope there is someone who has bought this device/gadget who is able to give me some advice and look forward to your reply.

Thanks in advance.

MHL adapters do usually need to be powered, yes. Power supplies / cables aren't usually supplied as you would typically use your device's charger to power the MHL adapter.

Also, have you checked that your device supports video output via an MHL adapter?