In my experience, it is a hit or miss proposition. I think you have to start with a serious audit of the power coming into your playback room. I live in a single family house. I had the meter pulled, made sure there was no corrosion (it's a 2004 re-do, with updates I did, of an 1880's house). The power where I am in Austin, proximate to downtown, is better than what I experienced in the lower Hudson Valley- say 20 miles north of NYC- largely due to the age of the infrastructure. That said, I took steps to make sure what power was delivered was as good as I could get it within reason. I had the main service panel gone over, replaced breakers where necessary, installed a separate sub-system for the main system which takes 60 amps from the main household service and feeds a big iso transformer via 4 gauge to the service panel next to the listening room. From there, I run dedicated 10 amp lines. This is all consistent with good practices.
I'd say relying simply on what the local power utility delivers can be hit or miss. You can be in a remote area, where there is little commerical activity and still suffer from power issues. I experienced that in two locations along the Hudson.
I'm not an advocate of "power conditioners" or "filters"-- I think you throw baby out with bath water. The large transformer probably does something, but honestly, the power here, even in close proximity to downtown Austin, is much better than what I experienced in a low density village along the Hudson River north of NY.
Part of it may be who you are sharing a transformer with. There are a couple of old apartment complexes adjacent, and I don't share power from the utility from either of them.
Here's the Iso-transformer. I am not suggesting that it is a magical solution but I like having it:
