Yamaha DTXpress/DTXplorer/DTXtreme

I've been playing my DTXpress (original model) with my country band 
for 18 months now, both at practice and at gigs.  It has been a big 
success.  But the thought has suddenly occurred to me: What if the 
12 volt DC power adaptor should fail?  Then we would have no drums! 
Has anyone been caught out like that?  I am thinking I should buy a 
spare power adaptor, just in case the first one should fail.