use a variac? I would never buy that unless I was getting heavy into some really specific stuff, unless it was for work
most people will buy a drive, or use a variac.
for mains SMPSU you could use a higher voltage power supply and skip the recifier bit and just work on the DC DC or DC ac converter.
The things in front of the DC rail are hard and expensive to test IMO. Active rectifier is a interesting use that might benefit from a high end AC lab supply for DIY... and I guess the PFC.
and I did not mean to get a chroma instead, I just mean that if you compare it to a chroma you see what its worth and if its highly deficient in anything. That supply is still really expensive (but I find mains extremely dull compared to something interesting like RF)