A shielded isolation transformer can reduce common mode noise by as much as 12 dB. A balanced (60+/-) iso transformer can reduce common noise by as much as 20 dB.
Differential or transverse noise is more difficult to reduce but when it comes to power transformers, the idea is the opposite of audio transformers. You want limited bandwidth and a EI core is better than a toroid in this regard. Toroids are easier packaging and have less magnetic radiation.
Transformers are probably no more or no less effective than LP filters for transverse noise below 600 Hz, which includes several harmonics. Personally, more concerned with high frequency SMPS hash.
Differential or transverse noise is more difficult to reduce but when it comes to power transformers, the idea is the opposite of audio transformers. You want limited bandwidth and a EI core is better than a toroid in this regard. Toroids are easier packaging and have less magnetic radiation.
Transformers are probably no more or no less effective than LP filters for transverse noise below 600 Hz, which includes several harmonics. Personally, more concerned with high frequency SMPS hash.