The Most Rev John Davies' comments came at the beginning Of Christian Aid Week 2018 which this year highlights the plight of the more than 40 million people displaced around the world, but who remain within their own countries.
Archbishop John, who is chair of Christian Aid Cymru, said in a video: "I want to make an appeal to you to recognise that, despite the behaviour of some, the good work goes on, and that good work needs your support, your generous support."
In February, Oxfam staff members in crisis zones in Haiti were accused of paying for sex among the desperate people the group was meant to serve.
"That behaviour sadly disfigures, overshadows and sometimes even hides the ongoing wonderful work which charities like Christian Aid do day in and day out to help vulnerable, underprivileged and poverty-stricken people around the world," Archbishop John said.
"This Christian Aid Week, if you see an event taking place locally, if an envelope comes through your door asking you to support that work, please be generous."
In Haiti, thousands of people regularly experience some of the worst natural disasters on earth.
In November 2016, Hurricane Matthew wreaked yet more havoc, killing 546 people and destroying homes, businesses and infrastructure. Up to 90 per cent of some areas were destroyed.
Christian Aid Week unites thousands of churches every year to raise money to support people in need worldwide.
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