Does a good power conditioner reduce need for power supply upgrade?

@sns +1

I live in an older apartment building in a neighborhood with lots of old homes being torn down and replaced with condos (cash registers). Even before the gentrification of the neighborhood, the power was iffy, maybe once every several months I'd experience a brownout and even rarer, a blackout. 

With all the new construction, there's been too many times that the power would go out and having my AQ Niagara 1200 in front of my gear provided protection as well as piece of mind. Those brownouts would cause flickering and surges as it came back on. Not good for anything plugged in. Getting something passive, like the AQ, wouldn't hurt. It clamps down when necessary and doesn't limit current. I don't see or hear any downsides.

All the best,
Nonoise

Years ago I bought an Audience AR-6 power conditioner.  I lived in a big city, the house was built in the early fifties and it really made a difference in in the sound quality. A few years later, I moved to the country in a new house that was built on what was a cow pasture. When I set up my hifi, I didn’t put the AR-6 in and I really didn’t hear anything bad. After a week-ten days, I reintroduced the AR-6 and heard NO difference, but I I kept it in for the magnetic breaker in it. Six years ago, I moved back to the big city, into a home built in 1962 and had to but the AR-6 In pretty quick. 
So I guess what I’m saying is can depend on where you’re living, how your house is wired, how your subdivision is wired and how many people you’re in your immediate area you are sharing with and for me now, I have a six story office building less than a thousand feet from me.

PC and equipment internal power supplies do have the common purpose of filtering out noise. Internal power supplies are entirely responsible for converting AC to DC and providing continuous voltage and adequate current, this affects dynamic capabilities of individual components.

I am a little confused.  By an external power supply, do you mean an audiophile quality power regenerator?  Let’s assume you do mean a regenerator like a Furman, PS Audio, Etc.  A power regenerator is designed to produce pure sine wave AC without the electrical and RF noise contaminating a mains supply and house electrical distribution lines.   A power conditioner is designed to filter electrical and RF noise from the mains and house distribution lines.  Putting a power conditioner after a power regenerator is redundant since a regenerator is theoretically producing pure power.  It will not physically harm equipment but theoretically not give improvement and possibly degrade SQ if there interference between filtering stages in the regenerator and conditioner.  I can only say experiment and determine yourself if there is an improvement.  I only use a conditioner that offers significant improvement in SQ.  
 

However, if you use power supply to mean your mains and house distribution lines, then improvements using dedicated breaker panels, panel surge protection, dedicated lines, and/or better outlets before a conditioner will improve SQ because you are providing cleaner power that will challenge the conditioner less.  Output after the conditioner will be cleaner.