"I can't find a schematic and cannot get the value of capacitors C356 & C358."
https://www.ssguitar.com/index.php?action=dlattach;topic=3805.0;attach=5777
C356 & C358 are .015/ 600V capacitors.
If the power supply cycles on & off that means it is trying to start but something is preventing it from doing so.
Typically, a short on the secondary side will do that.
By the way, this is a Switch Mode Power Supply.
If you have no experience with these it is in your best interest to take it too someone who does.
https://www.ssguitar.com/index.php?action=dlattach;topic=3805.0;attach=5777
C356 & C358 are .015/ 600V capacitors.
If the power supply cycles on & off that means it is trying to start but something is preventing it from doing so.
Typically, a short on the secondary side will do that.
By the way, this is a Switch Mode Power Supply.
If you have no experience with these it is in your best interest to take it too someone who does.