The power-driven vessel should change course and speed.
The power driven vessel should give way to the sailing vessel in most cases. The action taken shall be taken in good time, be obvious and seamanlike and should result in the give way vessel passing at a safe distance.
When a sailboat overtakes a powerboat, the powerboat is the stand-on vessel. (Ref: SB-29)
Powerboat
If you are operating a motorboat and your motorboat is being overtaken by a sailboat, you should maintain present course and speed. The vessel that is overtaking another vessel is the give-way vessel, regardless of whether it is a sailing vessel or a power-driven vessel. The vessel being overtaken is always the stand-on vessel.
The sailboat operator is the stand-on vessel so they should keep their course and speed while the PWC is the give-away vessel so it should change course and speed.
The question should be "When is the sailboat the stand-on vessel...? The answer is if the sailboat has an engine and if it is in operation, the sailboat is treated as a power boat in determining stand-on status. The right-of-way would then follow the rules for power boats.
When a sailboat overtakes a powerboat, the powerboat is the stand-on vessel. (Ref: SB-29)
When a sailboat overtakes a powerboat, the powerboat is the stand-on vessel. (Ref: SB-29)
Unless the sailboat is overtaking a power-driven vessel, the powerboat is the give-way vessel.
When there is a danger of collision, the "stand-on" vessel is the one that must maintain its course while the other must take avoiding action. Sailboats usually are the stand-on vessel when meeting a power-driven vessel, even if that vessel is another sailboat (if its engine is powering the boat, and regardless of whether its sails are raised or not). There are exceptions: if the power-driven vessel is "working," such as a fishing boat dragging nets, or the power-driven vessel is confined to a narrow channel due to its draft, then the sailboat must stay out of the way, by altering course if necessary. If a collision is imminent and the other vessel shows no signs of altering course, then the sailboat should take whatever course is necessary to avoid it.
A sailboat and a PWC are meeting head-on. Which one is the stand-on vessel?
When it's the least maneuverable vessel in the encounter.