X1000/x2000/x4000 are rebadged xli models for musician's friend.
The xli line is class A/B and has significantly better power supplies than the class D xls series. They also sound significantly better with decent speakers.
I know. Sam ash/guitar center( musician friend is tied with guitar center i think)has dedicated rebadge amps from both crown and qsc lines.
I think the PSU is fine on my xls 2500 it had no issues driving ultra low frequencies at max output all day. If the PSU wasn't all that great then I wouldn't be using it as a subwoofer amp for driving ultra low frequencies and rattling houses couple blocks away. I even tried it on difficult 2ohm loads and it had no issues if that what you're trying to get at.
I think you might be thinking of the Older xti models maybe. I know the older xti before, the home bench testing frenzy and complaints had issues with their PSU before xti was fixed by crown with the xti2 series. People were testing them against other amps and found issues testing the xti1000 with sub bass frequencies that would only output 15w@20hz before shut down. They did test the xls drivecore too and found no issues with outputting their rated power from 20hz-20khz. Forgot which site but, think can still find it.
I think I use pretty decent speakers ( I like them) which are reworked large altec lansing vott speakers. Could go into detail on their work but, I been babbling enough.