Besides DBS Vickers Cash Upfront having lowest fee for buy, what is an alternative brokerage having similar lowest fee for buy trade?

It depends on whether you want the stock to be credited to your CDP account, or held through a custodian.

For CDP, I believe DBS Vickers Cash Upfront is the cheapest at the moment. This does not apply for sell transactions, but you can link your CDP account to FSMOne to sell for similarly low commissions instead.

For custodian, there are plenty of options - Interactive Brokers (0.08% min $2.50), Tiger Brokers (0.08% min $2.88), FSMOne (0.08% min $10), POEMS (0.12% min $10). Currently both Tiger and POEMS have a no minimum commission promotion till the end of 2020.