Not sure about the GTR, but the Heat Island uses a 5.5mm x 2.1mm plug, this is 5.5mm x 2.5mm.
I couldn't find a VVPS with 5.5mm x 2.1mm in the UK/EU, so I got an adapter such as this one, works fine.
https://www.amazon.co.uk/kenable-Female-Socket-Adapter-Converter/dp/B004HTFCYY?th=1