RK100 is a isolation regulator which regenerates a pure sine wave output voltage, but I think ching are discussing step-down transformers in this thread.
Just bought a CSE TS-500S last week to replace my aged 600W 凱韻牛, the improvement is so dramatic and blows away the old transformer by 9 streets. Both the DAC and 09FD are plugged into the CSE, everythings come out cleaner and clearer with blacker background, higher resolution and wider soundstage. The performance is also further enhanced by putting the Oyaide INS-BS plus underneath. IMHO, it worths every penny and is one of the significant upgrades in my hifi journey this year. Couldn't image how it would become if the stock receptacles and fuse are replaced by better alternatives.