Not achievable with current tech, but there has been more interest in miniature fusion reactors lately.

The generally thinking is that it becomes easier to contain the plasma in smaller formfactors where the field strength is higher - a power plant would then be hundreds of tiny units working in concert rather than one big one. Of course, its fusion so nothing 'real' has come out of it yet, and it is unlikely something man-portable and energy dense enough to power iron man ever will.