Line6 PSU fairly hot

Rocker

Left it plugged in and the Pod was switched off. Discovered the PSU was warmer than warm to the touch. Even though it was not powering up anything. Unplug all in future....

Sassafras

Yes, it's bizarre, some PSUs do it, some don't. Probably @ICBM can explain why.

ICBM

This is why old 'linear' (transformer) power supplies have been effectively banned by the EU - not just because they get hot, but because it shows that even with no load, they draw enough current that when millions of them are left plugged in, the total power consumption is actually quite high - and there's also a thing called 'power factor' (a result of the phase relationship between voltage and current) which can be very high for an unloaded transformer and puts a greater strain on the supply as well.

Modern switch-mode power supplies have a much lower off-load draw and power factor. Dave @ecc83 may have comparative figures, I know that Blackstar switched from one to the other for their HT pedal range.