How would unlimited free energy affect the global market? What will the effect on today's global market if a new source of free unlimited energy was to be discovered?

How badly will it disrupt today's global market and how badly will it affect our currency?

Or it will do good to today's economy?
This would represent an extreme increase in long-run aggregate supply. In the AS/AD framework, this would result in a long-run increase in production growth and a decrease in the inflation rate.

How "badly" it will disrupt today's global market? You've built an assumption that it's bad into your question, but sure, it will be bad for anyone who has invested in current energy sources. It will be fantastic, however, for anyone involved in literally any other entrepreneurial activity.

The only disruption in such a sudden and unexpected technology improvement would be that some financial institutions would find themselves overinvested in the energy sector. Insofar as they cannot handle the financial capital losses, there may be a private debt crisis that pushes politicians to bail them out again (ideally using the increases in tax revenues caused by increased productivity), or to simply declare their debt null and void. This would cause some consternation, but given that people tolerated financial bailouts after the housing crisis (where financial assets were wasted without any obvious social benefits at all), it's unlikely that there would be overwhelming protest in such a scenario.

The negative impacts of such a productivity shock would only be temporary, however. Energy is one of the limiting factors of production, so free energy would cause production to grow as fast as entrepreneurs can find a use for it, which would be very quickly.