I've stayed in 5-star hotels around the world. This one simple, cheap amenity should be in every room.

• I've stayed in 5-star hotels around the world, but an amenity on a recent trip surprised me.
• My room at the Balmoral in Edinburgh, Scotland, came with a complimentary power adapter.
• It helped me realize that sometimes, the best amenities are the most simple.

The past few times I've gone overseas, my trip has begun in a frenzy.

Without fail, shortly before I leave for the airport, I remember I need a power adapter. So with my bags already packed, I frantically research what kind of adapter I need and tear through my drawers to find one that will (hopefully) work.

I've always found adapters slightly mystifying. Sometimes, they work; sometimes, they don't. Sometimes, I think I have one that's compatible with a country's outlets, only to find out it won't fit.

So when I checked into the Balmoral in Edinburgh, Scotland, last month, I was thrilled to find one sitting on the desk, awaiting my arrival.

A good hotel anticipates what a traveler will need before they can ask for it

In my time as a travel writer, I've stayed in hotels around the world — from five-star accommodations to airport chains.

I've stayed in hotels with Michelin-starred restaurants and members-only cigar clubs, and yet I found this simple, cheap amenity to be one of the most helpful.

It sounds silly: Wouldn't the best amenity be something a little more… luxurious? Of course, the Balmoral had its share of fancy services. It has a fitness center that would make gym buffs swoon, and a scotch bar with hundreds of whiskeys. These are the things that help a five-star hotel earn its rating.

But I think some of the best hotels are those that predict a traveler's every need.

We've come to expect snacks and drinks in our rooms for when we're feeling peckish or slippers for the morning walk to the shower. It's only natural that this kind of thoughtful treatment should apply to the more granular parts of a hotel stay.

Other hotels should take notes

Having a travel adapter at my disposal felt like one less thing to worry about when I got to Edinburgh. I could charge my phone or start work right away instead of having to head out on a hunt for an adapter (which I have done before).

A spokesperson for the Balmoral told me that the adapters are in every room in the hotel. Guests don't get to keep them, but they're useful during the stay.

The adapter, despite being so simple, was exactly the kind of smart amenity I think every hotel should have — five stars or not.