While it is true that Malaysia runs an apartheid regime that favours the Malay race (meaning a body of laws that codify preference for civil service jobs, grants, land ownership, certain licenses, language of instruction in school etc etc) as a means to secure the vote of the majority Malays - those philosophical/political differences aren't the reason why Singapore would prefer to purchase solar power from Australia rather than Malaysia.
Electricity generation in Singapore runs on natural gas which are fed from pipelines to fields in Indonesia and Malaysia. LNG ports were developed to create an international supply chain and a solar cable to Australia would be a similar geostrategic/economic strategy of diversification through multiple vendors.
Malaysia has, at any rate, sowed the harvest of their political strategy. The Malay population has crept upwards as a percentage of total population, as Indians and Chinese with any ability have left for Australia and Singapore as popular destinations. This has secured pro-Malay politics as the only way to win an election in Malaysia, but ironically the increased ground means the old monolith pro-Malay party has splintered to fight for control. Today's Malaysia sees several strong pro-Malay parties jostling for power.
Singapore would prefer nobody build a nuclear reactor anywhere near it. Even if a reactor was located 50km away outside of Singapore, any accident could divert shipping lanes away from the Malacca Strait and disrupt air travel that hubs in Singapore. A nuclear reactor strategy for Singapore is like picking pennies before a bulldozer.