If its in warranty, call Uniden and send it in for repairs, If it is out of warranty, you could start by checking the female dc plug port for a cracked solder connection or cold solder joint to the circuit board.
This is common to all scanners which are frequently unplugged and re-plugged in, and laptop computers too.
You will need to open up the scanner and get to the board, Look at it under good light with a magnifying glass or something similar and wiggle the connector, does it move? can you see a crack? Anyhow, the fix is to just touch each of the 2 connections briefly (already hot 20 watt soldering iron is more than enough, anything more powerful is too risky for melting the board), long enough for the solder to melt and thats all, usually I add a thickness or 2 of electrical tape around the connection to make it tighter in the case when re-assembled (kinda like roast beef between the two slices of bread).
If you are not comfortable or are unsure, take it to you local shop and ask them to check for you.
On my 246t I had a cold solder joint on the scroll pot, and within a day of them sending it back, a cold solder joint on the positive battery compartment to cicuit board wire.
No big deal, this is often what results in "REFURBISHED" electronics from any manufacturer. If I have the opportunity to but a refub I always will, it means it has seen a technicians desk and not just the manufacturing process.