How much does tube brand REALLY affect sound in terms of rectifier tubes?

The tube rectifier's job is to convert AC into DC.  If the load is greater than the DC supply, this will cause a voltage sag which results in a compressed sound.  My question is, if the pre or amplifier's rectifier is properly designed to avoid voltage sags, will changing the tube rectifier to a different brand, not type, affect the sound? 

Voltage sag and compression aren’t the only cause of changes in the sound of a component's presentation.  Mainly, that affects it’s dynamics. That’s why I said, "sometimes", that will improve with a rectifier change. The short answer to your question is, "yes". BUT- there’s much more involved than just a, "different brand" involved. Most of us that have enjoyed various aural improvements through rectifier upgrades, have been using higher quality, NOS pieces, manufactured decades ago. Given that relatively few newer components have been designed with valve rectifiers(and/or regulators), there’s not been much demand and little motivation to produce great ones, these past 30 years or so.

Thanks rodman9999.  Yes, very few new tube amplifiers are employing tube rectifiers in their circuit because of voltage demands.  I still see quite a few preamps that use tube rectifiers as the voltage demand is within the tube's capabilities.  I am just having a hard time understanding that if a rectifier is providing more than adequate DC current demand, how can a different brand of tube sound different if the DC electrical parameters are identical?  In any event, I going to try again, some different tube brands in my preamp. 

There are lots of things we can't understand , don't let the "facts"  trump 
 your ears .

There are a few companies now manufacturing tubes, that have tried to produce valves, copying the internal construction/design parameters of some of the most popular, from decades back. Mainly, what they’ve succeeded in duplicating(capitalizing on) is the marque only(ie: Telefunken/Mullard/Gold Lion/Tung Sol), as none genuinely perform like the originals. The time involved in hand construction, attention to detail and(in many cases) materials used, are no longer either profitable or(perhaps) available.Try some authentic, older, well reviewed valves(as mentioned above). Worst that can happen is you’ll have to turn them, should they not turn you on. It may cost a few bucks to experiment, but- what doesn’t, in the audio affliction/addiction? Our, "rewards" are SO subjective! Happy listening!