To append, some examples of high speed systems with multiple manufacturers.

🇪🇺🇬🇧: Eurostar has, for the Channel Tunnel, two types of train built by two manufacturers. The old type by Alstom, the new type by Siemens.

🇪🇸: Just AVE has three different builders. The S-101 by Alstom, the S-102 by Talgo and the S-103 by Siemens. The S-102 is also used by Avlo, while OuiGo used Euroduplex sets by Alstom, and Iryo uses ETR 1000 sets built by Hitachi Italy.

🇮🇹: The ETR 500 is built by a consortium of manufacturers, several of which have been absorbed by others. The ETR 1000 has been built by a chain of builders due to mergers n stuff. And the NTV units are built by Alstom.

🇯🇵: Pretty much every major manufacturer of rolling stock has built at least some Shinkansen units. You'll find trains by Hitachi, Mitsubishi, Kawasaki and others all over the network.

🇨🇳: The first generations of CHSR trains were all imported designs, derived from others, both Shinkansen and European types. This allowed them to kickstart a domestic rolling stock industry for later generations of train.

🇨🇭: Once we lower our standards of speed a touch, SBB uses two types, one by Alstom built in Italy, one by Stadler built domestically. And trains from neighbouring networks ride into particular areas, each of which has their own builders.