I made a rookie error and accidentally saved about 20 images in Photoshop as
.jpg files rather than
Is there a quick way I can convert all these files to a
.png format at once rather than individually?
Well, you are about to commit another rookie error.
There is absolutely no advantage in converting a JPG file to PNG.
The JPG compression is now applied to your file, there is no way to "undo" that. The only thing you are going to have now is a bigger file size with the exact same quality as the JPG.
The only reason to do this is if you process again your image to add a transparency, or in the remote case your application can only use PNG, for example in the case of a Gaming engine. If that is not the case do not do that.
You can automate the process by making "action" in Photoshop. Its called "Batch Process".
File > Automate > Batch
And you should be good to go.