It is not advisable to lie to your potential employer about your past employment as that could go against you, if a background check is conducted by the new employer.
As regards the NOC, you can't join another PSU without it. The current employer must grant you the NOC, provided you informed them before applying for the new job. They do not have the right to deny NOC in this case. If they still do so, you can file a written request to the authorized person, at least a week before the job interview. You can further, submit the copy of the request to the potential employer if you're not provided a NOC.
In case, the current employer remains silent and does not reply to the candidate despite the issue of reminders to provide NOC, then it is taken to be deemed permission to apply for another interview.
If you haven't informed them about seeking a job interview, you can resign from the job and pay the bond money to the PSU. You can inform the new employer that you have to resign and seek the Relieving order or Relieving certificate from the current employer as without NOC/relieving order, the new employer has power to terminate your employment. You may also ask the potential employer to provide you with a grace period to submit the Relieving order.
I hope the answer helps you.