GATE

The list of PSUs for ECE recruitment through GATE is listed below:
1- Airports Authority of India (AAI)
2- Bhabha Atomic Research Centers (BARC)
3- Indian Space Research organisation (ISRO)
4- NLC India Limited (NLC)
5- Hindustan Petroleum Corporation Limited (HPCL)
6- Nuclear Power Corporation of India Limited (NPCIL)
7- National Thermal Power Corporation (NTPC)
8- Electronics Corporation of India Limited (ECIL)
9- Power Grid Corporation of India Limited (PGCIL)
10- Oil and Natural Gas Corporation Limited (ONGC)
This can't be answered in the exact figure as it depends on the number of vacancies available in the Public Sector Undertakings. But if roughly estimated, including all Maharatna and Miniratna PSUs, It would be around 150 to 250, which varies per year.

GATE is also a qualifying test for many PSUs for ECE engineers. However, the following public sector units are recruiting through the GATE as well as sometimes they conduct their own exams. AAI- Airport Authority of India. BARC-Bhabha Atomic Research Centre. BBNL- Bharat Broadband Limited. BEL Bharat Electronics limited. BEML- Bharat Earth Movers Limited. BHEL- Bharat Heavy Electrical Limited. BSNL JTO- Bharat Sanchar Nigam Limited; Junior Telecom Officer. CEL - Central Electronic Limited
DMRC- Delhi Metro Rail Corporation. DRDO- Defence Research and Development organisation. ECIL- Electronics Corporation of India ltd. HAL- Hindustan Aeronautics limited. IOCL- Indian Oil Corporation of India. ISRO- Indian Space Research organisation. MDL-Mazagon Dock Shipbuilders Limited. NTPC - National Thermal Power Plant. NHPC- National Hydroelectric Power Plant. NLC- Neyveli Lignite Corporation Limited. OMPL- ONGC Bangalore Petrochemicals Limited. I hope this will help you.

Eligibility Criteria: A student who has already completed any government-approved degree programme in Engineering, Technology, Architecture, Science, Commerce, and Arts is eligible for appearing in the GATE exam. There are a total of 29 subjects in the Graduate Aptitude Test in Engineering examination. A list of all subjects with code is listed below:
AE: Aerospace Engineering
AG: Agricultural Engineering
AR: Architecture and Planning
BM: Biomedical Engineering
BT: Biotechnology
CE: Civil Engineering
CH: Chemical Engineering
CS: Computer Science and Information Technology
CY: Chemistry
EC: Electronics and Communication Engineering
EE: Electrical Engineering
EY: Ecology and Evolution
ES: Environmental Science and Engineering
GG: Geology and Geophysics
IN: Instrumentation Engineering
MA: Mathematics
ME: Mechanical Engineering
MN: Mining Engineering
MT: Metallurgical Engineering
PE: Petroleum Engineering
PH: Physics
PI: Production and Industrial Engineering
ST: Statistics
TF: Textile Engineering and Fibre Science
XE: Engineering Sciences
XL: Life Sciences
XH: Humanities and Social Sciences
GE: Geomatics Engineering
NM: Naval Architecture and Marine Engineering.

The GATE is a national-level exam which is conducted in India that primarily tests the comprehensive understanding of various UG subjects in engineering and Science for admission into the M.E. /M.Tech. Ph.D. programme and Job in PSUs. However, the GATE exam is not conducted for JRF. The NTA has been entrusted by the UGC with the task of conducting UGC NET which is a test to determine the eligibility of Indian nationals for Assistant Professor and JRF and Assistant Professors in Indian colleges and universities. NET is a national-level test of the UGC for the award of a JRF to eligible students. PG students, who want to undertake research studies in the field of Engineering, Science, Humanities, Social-Sciences, or more can apply. I hope this will help you.

Electronics and Communication Engineering, Mining, Physics and Electrical are the toughest branches for the Graduate Aptitude Test in Engineering because of their competition. Lacs of students appear in the examination every year and due to this, the level of difficulty of the examination has risen day by day. The difficulty level of the GATE exam:
Electronics and Communication Engineering: Moderate to Difficult
Civil Engineering: Easy to Moderate
Electrical Engineering: Moderate to difficult
Mechanical Engineering: Moderate
Computer Science Engineering: Easy to Moderate
Mathematics: Easy to Moderate
Biotechnology: Moderate
Chemical Engineering: Moderate
Geology and Geophysics: Moderate to Difficult
Agricultural Engineering: Moderate to Difficult
Chemistry: Easy to Moderate
Physics: Moderate to Difficult
Architecture & Planning: Moderate to Difficult
Aerospace Engineering: Easy to Moderate
Mining Engineering: Difficult
I hope this will help you.