Components such as transformer, bridge rectifier, capacitors usually all have isolation so they can be mounted directly to the enclosure and the enclosure should be connected to the incoming supply ground wire, some capacitors have the case at ground and if so should be insulated if you require a floating power supply ground, but most of the large capacitors intended for power supplies have isolated case. I usually ground all my power supplies by connecting the negative output of the DC supply to ground (enclosure). The think to watch for in aluminum stand offs is that they do not touch any of the foil on the circuit board.
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.