If its a transformer, rated for enough power, yes.

Some cheap, small, traveller's adaptors are solid state switching devices that only pass part of the AC waveform. This reduces the amount of power drawn from the output, but the waveform is an ugly thing, with a lot of strange harmonic content that usually causes a lot of hum or buzz. This kind of adaptor is meant for use with electric shavers, or laptop computer 'wall warts' that don't much care what the power 'looks like'. I wouldn't expect to find this kind of adaptor working well with a stereo, (much too noisy), so yours may be OK. You still need to consider the power rating.

The Fender web page didn't show the VA requirenent of the Blues Junior, but I expect it is something like 60 to 80 VA. When you don't know for sure, its best to be on the safe side with your estimate. I recommend at least 100VA.