I was an Audible Illusions dealer and currently use a M3A+ as my reference preamp.
Pretty sure there isn’t an additional fuse inside the power supply.
Do you have the newer power supply with the on/off switch or the older one without? Some of those switches have failed. Could be a bad switch, if you have one.
You said the fuses "seem" okay. Do you have a VOM so you could check for sure?
Sorry you’re having issues.