Understanding a power source's internal resistance?
Whatever the power supply might do internally is not relevant to you.  If it says it will supply 10 A at 10 V, then it will supply 10 A at 10 V.  Of course none of these supplies will be 100% efficient, so it will take more than 100 W in to produce that 100 W out.  This extra input power has been taken into account in the spec that says what maximum current the supply will draw at certain line voltages.  The fuse will also be sized accordingly.

Otherwise, a power supply is a "black box" that you shouldn't make assumptions about how it works internally.  It specifies what goes in and what comes out, but other than that you don't know, and it's none of your business, what goes on inside to accomplish that.

As a separate topic, if your mechanical system requires exactly 100 W of power, then specifying a 100 W power supply is not leaving any room for anything to be a little degraded or for stuff to happen.  This is bad engineering.  What happens when the bearings get a little worn, there is a little more friction than you expect, etc, etc?