Stand alone power supply

Hi all

Im new here and a complete novice regarding electronic design but I am interested in learning so I can build my own amp. I like the idea of a pure class A running off a separate power supply

Can anyone here tell me what the advantages and disadvantages are of having an outboard power supply? Apart from cost, my understanding it that if the transformers are kept at a distance it dramatically improves interference?

If running long cables to carry a dc voltage to the amps what are the problems likely incurred? Im thinking rf interference unless screened? I know the likes of naim claim outboard power is the only way for hi end sound.

Any advice and opinions greatly appreciated