I've just been repairing a linear PSU where the toroidal transformer had failed due to a faulty 0.1µF disc capacitor across one of the rectifier diodes which had gone short circuit. The insulation on one of the low volt outputs from the transformer had melted - so it was obviously drawing excessive current before it failed.
It's a 28 volt regulated 1 amp PS made by a long defunct pro audio company. The regulator is an LM317T, and it has an adequate heatsink and has survived. The transformer a 15 + 15v 30 VA. No LT fuses, only mains (240v, 250mA standard type.) which had blown.
Now toroidal transformers have a high 'startup' current, so I'd guess an anti-surge would be better at perhaps 125 mA?
Is there a 'rule of thumb' for mains fuses for such devices? And this isn't the first disc ceramic I've come across which has failed short circuit. Better type?