Hi I don't see to find any info regarding csync been actually available from the gpu on the PSOne, most posts talk about H and V sync only.
Here is a little diagram I made. https://ibb.co/dM3qca (https://ibb.co/dM3qca)
(https://thumb.ibb.co/dM3qca/SCPH_101_csync.jpg) (https://ibb.co/dM3qca)