One of my relatives has been working with NTPC for the last 36 years and he advises against it. According to him, it will not be a good decision to leave NTPC to pursue a course at NITIE. But if you want to pursue a career in management you can go for NITIE. On completion of your course, you will get salary packages similar to NTPC.
NTPC is one of the sought-after PSUs and can be the best place to work. But it also depends on your interests. If you want to go into Management work and feel trapped with PSU, then you can surely join NITIE.