Update - and kudos -
First, we want to thank everyone for the kind, informative and useful information. Since the Forum platform seems to think I've already "thanked" many of you too many times to do it again, I'll do it here - you know who you are!
Additional kudos - to Amazon, believe it or not. Found a highly-rated 30/15 adapter for a good price, and pulled the trigger on the order. It sat in my storage for a week before I pulled it out to use - and found the 30f connector was wrong layout (note to self - attention to detail!). Went online to process a return and order the right one - no issues with that process.
Amazon not only credited my card almost immediately, but due to the value of the item - told me not to bother with return! (So, I have something in my road stash to "pay it forward" down the line). Replacement arrived today, and batteries are currently topping off on shore power.