These are original, NOS power transformers that were used by MXR in the 1970s and 1980s for their AC powered pedals like the Flanger. Great for replacement in vintage MXR pedals or for use in new designs.
In the MXR-style half-wave power supply circuit on my breadboard it put out 18VDC with a +12v regulator and a 470 ohm load for 25mA of current.