A retired aircraft technician who killed his wife of 36 years during a psychotic episode will spend more time in prison after the Court of Appeal raised his sentence from two years to six.

The three-judge court stressed yesterday that the longer jail time was not to punish Kong Peng Yee, 70, but to rehabilitate him and prevent him from harming others.

"We believe that an imprisonment term of six years will give the respondent sufficient time to become accustomed to the new reality of having to take medication in a disciplined manner," said Judge of Appeal Tay Yong Kwang, who delivered the judgment.

Hopefully, this will be of "great benefit" to Kong when he is freed and returns to live in an uncontrolled environment, said the court.

The court rejected the prosecution's argument for a nine-year jail term, premised on the principles of deterrence and retribution.

"We think a sentence of six years will also assuage, to a reasonable degree, any concerns that the public might have about a potentially dangerous man living in its midst, especially someone who killed his wife of more than three decades in a most brutal and violent manner only slightly more than two years ago," it said.

Kong's sentence was the shortest ever meted out for intentional culpable homicide in Singapore.

Kong started having delusions that his family was trying to harm him in 2016. On the afternoon of March 13, 2016, he woke up from a nap, took a knife from the kitchen of the family's home in Sengkang, and stabbed Madam Wong Chik Yeok, 63, until she was dead.

He then told his sister to call the police and wrote on a piece of paper how his assets should be distributed.

An autopsy noted 189 injuries, including knife wounds and bruises, on Madam Wong.

Kong told police he believed he should kill his wife first because his family might want to kill him.

Remanded in custody since his arrest, he was released from prison on the day he was sentenced, in October last year. He has since remained at the Institute of Mental Health as a voluntary patient.

Taking into account the usual one-third remission of a sentence for good behaviour, Kong will have to serve another two years and five months in prison.

In arriving at its decision, the court looked at various sentencing options and settled on a longer prison term, saying it was in the public interest.

"In prison, he will have free and easy access to psychiatric services, live in a structured environment, and be subject to the supervision of trained staff who can ensure that he consumes his medication and assist him along the path of recovery," said the court.