In troubleshooting a SMPS I found that the transformer isn't being turned on, on the primary side. The rectifier has 172vdc and all of the passive components and diodes look good on the primary side. A ceramic safety cap coupling, what looks like maybe, a feedback signal ( I don't have schematics so I may be wrong), has appropriate capacitance ~47nF but infinite ESR. Normally I'd say it's definitely bad, but I'm not sure how safety caps work in regard to an ESR meter. Should it look the same as a normal cap? I don't have any to swap it out with and wanted to know if anyone could enlighten me before I place an order for parts.