A DC power source unit supplies a DC voltage to a power tool through an adapter when a power switch of the tool is turned ON and also charges a battery pack used as an alternative power source of the tool when the power tool is not operated. The electrodes are coaxial and cylindrical and overlap axially along part of their lengths. Where clutch disengagement occurs before the loop times out, skip shift diagnostic execution is enabled. X1 and X2 each represent a substituent selected from the group consisting of a hydrogen atom, an alkyl group, a methoxy group, and a cyano group. After the tubes are telescoped together weld current is conducted through the tubes to weld the annular projections to the respective opposing tube in contact therewith and at least partially cure the adhesive. The current output circuit includes a current source for providing a driving current, and a first output circuit coupled with the current source.