Hi
As far as I know the only way to get a unlimited world wide approved DP operator certificate is through the training scheme laid out by Nautical Institute (NI). So actually it doesn't matter which training center you choose as long as it has its accreditation from NI.
Some of the DP manufacturers, have their own training centers, but it is only meant to give equipment specific training for crew manning newbuilds. They may give a induction course to their specific DP, but you will not qualify for a DP certificate.
A list over training centers around the world approved by NI, can be found
hereNI is, to my knowledge, at the present, the only organization issuing DP operator certificates.
A guide to the DPO certificate can be found
here If you require more information feel free to ask