Bill, I have owned the VK-500 with BAT PAK, the Cary 500MB, and currently the Cary SA-500.1 monoblocks, which are essentially two of the SA-200.2 stereo amps, with different input modules.
All of these have pretty good power supplies and the newer Cary amps improve the power supplies even further over the 500MB, since they doubled the heat sink area, included a 1,500kVA low noise transformer (my 500MB transformers displayed mechanical hum while my 500.1s are quiet), and improved capacitance and current, as stated by Cary,
dramatically improved performance and current-handling capacity over our previous models
I suspect there are further improvements of the SA-500.1 monos over the SA-200.2 stereo version (which I have not heard), that go beyond the substantial increase in power since the 500.1s would be a dual differential design with the two halves each driving one phase resulting in the substantial increase in power and better noise cancellation.
The other basic design difference between the newer Cary amps compared to the 500MBs are the use of a larger number of smaller capacitors located closer to the output devices, rather than the fewer large capacitors used in the 500MB. They have increased the overall capacitance.
A distinguishing design difference between the Cary amps and the BAT is that the BAT uses mosfet devices in both input and driver stages and the Cary amps use bipolar output devices. You can do searches as to the characteristics of these devices but some would say mosfets have a softer presentation and bipolars have better detail and slam - as a gross generalization.
Regarding how the amps sound, in my system, the BAT did indeed have a sort of softer pleasingly warm midrange at the expense of some definition and HF extension. The bass was quite solid but a bit "woolly." The 500MBs had a sweet sounding HF, and a smooth, rich midrange that many like, but the bass suffered from a lack of control and was somewhat plump as a result. The 500.1s improve on the 500MBs dramatically in the bass, which is as good as I have heard, and also improve in the areas of clarity/resolution, soundstage, and dynamics, while having a much lower noise floor than I experienced with the 500MB.
In summary, they are all ok but I would tire of the BAT over time and would choose the 500MBs over the BAT, and certainly the 500.1s over the 500MBs, as they are pretty much better in every way.