Generally if you plug it in while you're not using it, a lower wattage charger will still charge the laptop more slowly. If you are using the laptop, it will sometimes not charge, sometimes will discharge faster than it charges. Just depends on the circumstances.

The number one reason I use the extension cable on mine is that I can get a firm connection in the notoriously loose airline power sockets. The normal Apple brick would fall out constantly on older aircraft, while the extension was much more secure. Having the extra length is also useful sometimes for hotel rooms and lounges without convenient power.

I bought the PD version of this, carry it everywhere when travelling

https://oneadaptr.com/pages/meet-oneworld

Thanks, but at 18w it is not going to charge my macbook

I would recommend something like this:
https://smile.amazon.co.uk/Anker-Cha...dp/B07ZGHB8SM/
45W USB-C PD will charge (and run while using) most any Mac - even the ones supplied with a higher power adapter from Apple will usually consume less power, so unless you're using all CPUs and the GPU full time in flight it will work fine. For a 13" Macbook Pro, even 30W PD will suffice for general use.
Power input is IEC C7/C8 so either use the supplied cable or carry your own. The other USB ports can be used for iPods, phones, headphones, etc, etc.

I have been carrying three short cables for years: Euro, UK (Singapore, etc) and US to IEC C7 - all used to connect my Magsafe-2 charger. When I eventually get a USB-C powered Mac, I'll just get a device like the above one and keep carrying the same cables.

Note on vendors: I have no interest in Anker or Amazon, but in my experience as a customer Anker has consistently high quality but is not high-profile enough to be faked so if you buy Anker on Amazon (from "Anker Direct") then you do not get an unsafe device. This is, unfortunately, not true for Apple-branded power supplies!

I was unable to use that product to run my 2018 MBP 15 inch model whilst doing running pretty basic Python code, it just kept draining.

The moment I started doing some GPU accelerated stuff it completely failed using that power dropped so fast it was as if I wasn’t even using a charger.

Apple still sell the power extension adapter cable, but they no longer include it with every laptop purchased (which makes sense since you probably have one from your old laptop). You can buy them from the Apple Store in the UK for £19 (incl. shipping).

Thank you!!!!

I didn't even realise my old extension would work with the new power lead!!

Guess I never tried it!

Hm. I am using a 2017 touchbar MBP 13 inch with 4 TB ports, under Bootcamp and Windows no less, and I have NEVER used anything other than a 45W Mu One USB-C charger, and I have never had it drain power faster than it was replenished. At the desktop, I am using a dock - that's where the battery of outputs and dongles tends to suck more power.

So I wonder whether there really is that much of a difference between the 13in and the 15in, or whether my workloads are really that low - I do run VMs, but I don't do much in terms of graphics...

There definitely is a difference, I bought a 2018 13" MBP which was supplied with a 61W charger. My business partner opted for the same model but the 15" version and was supplied with an 87W charger.

Also, to those looking to buy an extension cable, please don't waste £19 of your hard earned cash buying an apple one. As has been said previously, any old figure of eight power cable will suffice, such as this one for £4.99

Cables aren't indestructible and if that was really the driver they would give you a choice to have the cables for free.

I kickstarted one of these (took about 4 months to arrive, allegedly due to covid) but I expect now they're producing / shipping a bit more readily.
https://www.hypershop.com/collection...-c-gan-charger

If you have a larger (15/16") MacBook then you need closer to 100w of juice to charge -- I took this on holiday recently and it was brilliant to charge an iPad, watch and two phones all from one outlet (which often is all you get in some places!)

So far quality seems very good and it doesn't get hot when in use which was my main concern. It's similar in size to a deck of cards, maybe a touch bigger.

But yes more directly for the OP- the longer lead that Apple used to ship with the laptops is a must have IMO if you don't know what the plug situation is like. It's also useful to extend the reach of the more traditional Apple chargers in hotels etc.

https://www.kickstarter.com/projects...arger/comments - not so good comments here

Not disagreeing with anything that was said, as this all needs to be appropriate for what people are doing with their laptops, but I maintain that a lot of people are carrying around power bricks that are far too big and heavy for their needs, just because they look at what came supplied and try to match or exceed it, with a lot of people (my colleagues) not even realizing that third party chargers are a thing.

I have quite successfully charged a Macbook from a phone charger(!) overnight, obviously while turned off. I think this sums it up quite well for a Macbook's power consumption:
So for normal office workloads, a 45W power supply is plenty to power the laptop AND keep it topped up. If a workload exceeds that for a while, the battery might deplete (never seen that in real life), but would soon be topped up again. Of course playing games, encoding videos etc. would be an issue, and that's why all laptop vendor bundle ludicrous power supplies, but ever since I experienced the Dell "Travel" Power Adapter vs. the one shipping with it, I realised that there is no need to carry around a kilo of a power brick...

Realised the other option for the OP would be to grab one of the international 'duck heads' for your Mac charger which would then work in either 'up' or 'down' orientation (e.g. the US or EU head).
I carry these with me when I travel as well to minimise the need for chunky adapters if I can:
https://www.apple.com/uk/shop/produc...el-adapter-kit

I bought this 'apple travel adapter' set a while back, which while overpriced, I trust from an electrical safety perspective!
Word to the wise though- don't try to force the Korean plug into a European outlet like I did (It fits in some, but not others). There's a lodge in Zermatt which might have a permanent fixture left behind by me :(