I think that we have been pursuing two different lines of thought on this, and it relates to whether one is, as
@Leanne Lang was, preparing for one's pilgrimage, or looking for an urgent replacement of a charger misplaced during it.
I don't expect anyone from Australia, NZ, the US, Canada, the UK or even the rest of Europe to do a quick trip to Spain to travel at a two-dollar shop to buy a multi-port USB charger. That doesn't mean that they cannot shop for the equivalent through eBay or Amazon, but they will have access to a range of devices at conventional retailers that have been certified within their national standards frameworks before they can be offered for sale.
The advice that one should prefer an OEM device in these circumstances is not justified by the evidence.
If members are going to use an on-line shopping service, my advice would be to look for the certification marks that have been printed on the device. These may be national approvals, the CE symbol for the EU, a Regulatory Compliance Mark or its equivalent, RoHS, etc, etc. My current 4-port universal adaptor has the CE and RoHS markings, but the design does not comply with all the Australian certification requirements. It performs better under load than the Samsung travel adaptor that came with one of their tablets, as does a similar device I use at home. I will replacing the travel adaptor before I next travel to Europe with a higher capacity device that will support USB-C fast charging.
I have checked both eBay and Amazon, and there are devices which appear completely devoid of any certification markings.
My view is that these are best avoided.
Others carry a range of certification markings, most commonly the CE and RoHS symbols. That would suggest that they have met the EU certification requirements, and would be a reasonable choice., even though they may not meet all of the national certification requirements around the world.
And the reason for needing a multi-port charger is not complex. I have several devices to charge besides my phone. If I took individual OEM chargers with their Australian configured electrical pins I would need plug adaptors all at additional weight, and would have to find several wall plugs wherever I was staying, or be up and down all night swapping charging devices around. None of that sounds great when I could use a single universal travel adaptor.