You can export the security policies from the NSX U.I in CSV format 

yes that option is there but i was looking for a better formatted data. As the one we get from the gui export is little more of data which again needs to be formatted per requirement.

Another option would be to leverage VMware Aria Operations for Networks

Thanks i will explore vrops and see if it suffice my requirement.

Not PowerCLI, but you should be able to retrieve all DFW rules through the API as well.  

Loop through this to get all policy id's:
GET /policy/api/v1/infra/domains/<domain-id>/security-policies

Then use the results to loop through this to get an overview of all the rule-ids within each policy:
GET /policy/api/v1/infra/domains/<domain-id>/security-policies/<security-policy-id>/rules

And finally, you could loop this to get the details for every rule within the policy:
GET /policy/api/v1/infra/domains/<domain-id>/security-policies/<security-policy-id>/rules/<rule-id>

This should allow you to output it all in JSON. 
Alternatively, consider managing the rulebase through IaC, that should give you a permanent overview of your rules in a repository.