No physical computer is a perfect Turing machine, thanks to random noise.

Analogue computers can always implement a Turing machine to within the bounds of that noise (and that's how transistors, which are really analogue devices, get used for digital signal and information processing).

A computer that used infinite-precision real numbers would be more powerful than any Turing machine, however unlimited-precision real numbers in the physical universe are prohibited by the holographic principle and the Bekenstein bound so we can't have them.