I have an engineering degree (MEng) and some work experience in my field ( only in academia though not in companies).

I want to do an MBA because I am interested in the administrative side of big engineering companies.

Will it be better for me to do an MBA with specialisation (like Innovation, International Management etc) rather than just an MBA? Will this help me better, since with the specialisation, I will gain the knowledge of those topics?

Or does a simple MBA covers those topics anyway?

Take a look at http://find-mba.com/board/general-forum/specialisations-dont-often-matter-42969

I don't think that those specializations -- innovation and international management -- are really necessary for administrative work in an engineering company.

If you wanted to work in something that's more specialized, like as a supply chain manager or perhaps something operations-oriented, there's real value to doing a specialization.

Ultimately, it depends on what you mean by "administrative side," because that's quite vague.