Power difference between automatic and manual?
 

First, I did try searching for this, to some extent. Did not really find anything.

Now, in the past, if I remember correctly, vehicles with automatics would output less power than manuals since some of the engine power had to be used for switching gears in an automatic. I was curious if that is still the case today. How much power can be expected to be lost at the wheels with an automatic transmission or is this a thing of the past?

Unless you dyno in first gear it should read more or less the same on a dyno. Normal variance. If there is a power difference it'll be slight, especially compared to old autos without a locking TC.

The gear ratios are taller on the automatic (not sure about the final drive). That is where the biggest performance difference will stem from on the street and the dyno.

But still, does not the automatic need power from the engine to switch gears? And if so, would that not mean less power to the wheels? I would imagine a few horsepower loss at the wheels. Do not know about torque.

I'm not an AT guy, but it's electronically shifted through solenoids I believe.

A pump inside the A/T generates line pressure. This pressure is manipulated in the valve body for applying pressure to various elements inside the A/T. You would really have to do back-to-back dyno runs on A/T and M/T vehicles using the same dyno.