James Sweet wrote:

If the user-accessible part of the chassis is metal then that has to be
bonded to mains earth.
2 core is only allowed for double insulated kit in the UK.
Its not a quality of sound issue but a health and safety issue first and
foremost.

I've never seen a piece of consumer A/V gear with a grounded power cord,
regardless of what the case is made of, but it certainly won't hurt anything
to ground it.

It MAY create problems. A grounded case will almost certainly ground the outers
of the RCA jacks. That will provide a path to ground for any leakage currents
and in turn that may result in 'hum' as currents flow where they weren't
intended to.

Graham