The SMPS180 has a Power Factor Correction circuit that the SMPS400A180 does not have, also the SMPS180 has adjustable output of 2 X 35VDC to 45VDC, whereas the SMSS400A180 has fixed 2 X 46VDC output.
Not sure why you might want to use it though, or what improvement the PFC might give. My impression is that the SMPS180 came out first and was later followed by the SMPS400A180 and SMPS400A400 supplies that were specifically matched to the UcD180 and UcD400 amplifier modules.
Steve