It sure looks like EGA, not that Wikipedia is infallible (God knows!). With 640x350 capable of accommodating 512x342 (whereas CGA doesn't) and a Horiz. freq. of 15.7/21.8 kHz (which is pretty close to 22.3). All that would be required of the Power R adapter would be accounting for the additional blank lines to drive a standard EGA monitor. Perhaps that's what it does.
I find it difficult to believe that Power R would use a standard so foreign all the way until 1994 with the Classic II without updating it by 1998 (note the date of the product list on the Powerr.com site and the specs on the Classic II adapter which are identical to the SE & Plus). VGA quickly became the standard following its introduction in 1987, with EGA having been around since 1984. I can certainly see even by the 1990 release of the Classic adapter, maintaining the EGA standard which would have accounted for most of the available displays on the market since 1984.
If that's the case, I need to find an EGA monitor to try it out on. Ebay? What am I looking for? If it is EGA, then shouldn't I be able to easily convert from EGA to VGA? Update: a quick Google search suggests there would be nothing easy about it as the sync rate and resolution would have to be compensated for. Assumed that with all the EGA video cards, a cheap adapter would have been available in order to upgrade monitors, something likethis custom item.