All the outlets are 120v and needs genny or shore power. Unless you have an inverter installed on some of the outlets. Then make sure it is turned on/connected correctly.
Inverters are sometimes optional from manufactures in the era of your TH, but mostly aftermarket accessories. The built in ones might have a switch or breaker mounted somewhere...
Imo, the stereo should work on 12v. How are your batteries doing...? You know what voltage they are at when you try to run the stereo..?
Most newer stereo's won't run when the voltage gets low. Your lights, water pump, etc will run, but a little on the slow/dim side.
It makes sense that the stereo runs when on shore power, since then the convertor is supplying 12v to a possibly bad battery bank, just one possibility...>
Check your battery bank.
jmo
2007 WW FSW3200
RZRS k&t Turbo
2 LT500
1 Lt500 hybrid
F350 CC 6.7PS Platinum