no need solder one what... its only screwing to make sure contact is firm.
if ur power cable is detachable, u can jus go buy a 3 pin power cable from simlim, or if its not u can cut of the 2-pin head and solder a 3 pin head one
for a clearer picture of wad i said go here,http://soft.com.sg/forum/gear-guitar/7982-changing-2-pin-plug-3-pin-plug-grounding.html
Why can't i just buy another power cable which has a three pin plug?
Rather than converting a 2 pin to 3 pin?