Nvidia have a plugin that can convert height map to normal map, but the plugin non longer works with the latest Photoshop (I never got it to worjka anyway). But luckily, Photoshop provide one that does the job pretty well, allowing you to adjust the intensity level as well as the height .
Go to Filter->3D->Generate Normal map.
You will want to checked the invert height checkbox, & the reason is that in another classic case of lack of standardization, the direction of height (green channel) of the normal map differed from application to application.
In any case if the height/depth is wrong direction, you can manually correct it by invert the green channel (Control+ I).