i spent a week or so in great britain recently. when the battery died on my sp, i plugged in the converter and when i plugged in the gba sp charger, i could hear a faint buzzing noise coming from it. being stupid and desperate for some metroid fusion, i decided to try it anyway. i plugged the sp in and... nothing happened. the charge light did not come on, nothing. YMMV, but i was unable to charge it. when i got back to the u.s., everything worked fine, so its not really a question of things blowing up, just things not working. for what its worth, the converter i got was a samsonite.
my suggestion? order a couple spare batteries from nintendo, and charge them before you leave. dont forget a small screwdriver so you can swap them out.
have a safe trip!
~perth