Which do u think is a better power amp? Cary Cad120s vs vtl st-150?

The 120S is really quite different from most other Cary amps, and comes across as a much more detailed sound. It’s not the typical "tubey" Cary sound (which I love).
Having said that, I’ve never heard the VTL you mention, so not a clue how they compare to each other.

You have a Cary Preamp so Cary Cad 120 would be a wise choice for ultimate synergy. If you’re looking for a change, consider Ayon amps. Like, Ayon’s Triton Evo PA amp. Based on my listening experience, Ayon is a much better sounding amp over ARC, VTL and VAC.

I currently running a Cary cad 120s in the system but I was offered a vtl st-150 for $2500 but dose the Vtl run in class A in triode like the Cary?

Many like VTL but their customer service is horrible towards people who buy used VTL.   Only company in 40 years in this hobby that I had a truly horrible experience with.   

I have had only a handful of failures over the years.  Most gear is reliable today , but if something does happen you want a company that is known for exceptional service.