Q. What is the dissimilarity between isolation transformers and step up or step down transformer?

Answer:-

In fact an isolation transformer may be physically the same as a Step up/Step Down transformer. The major difference is in the way they are used. One more difference is that in a normal transformer there will be capacitance between the 2 windings among the windings and core between the core and shell etc.

These capacitances bring in elevated frequency noise from outside which will be transmitted in the secondary circuit. Therefore in an isolation transformer wires are connected between each component not direct contact but with insulation present. This allows a leakage current as well as eliminates unnecessary capacitance.