Problems with reusing the wrong power supply is why this article exists on the Virgin Media help site:
Checking your router has the correct power supply
http://help.virginmedia.com/system/v...A-FA750E63B96A
It was more of an issue going from the older modems to the SH1 - as you've found the SH2 and SH2ac have a different connector, as does the Hub 3.0