advice needed. Oppe phone charger broke.

Beyond 6 months from purchase receipt up to 6 yrs after (5 yrs Scotland): repair / replace / refund, where trader can choose to do jacks hit until you provide proof that the cause of the bustedness was present on the original day you took possession,
which normally involves the consumer commissioning a report from a qualified and credible expert to confirm that the product has busted prematurely due to inadequate durability present from day one, and has not been otherwise busted by being chucked down the stairs or not survived being chased around your garden by your vicious pet goldfish.

If the goldfish is proven innocent the merchant must pay for the report, plus repair or replace the product at the merchant's preference, or pro-rata refund referenced to the product's expected longevity had it not busted prematurely.

Anything beyond above is gesture of goodwill.

That appears to be a phone launched in 2017 so how long between purchase and raising the issue with Currys could be important as you're close to the 5-6 year expiration date for consumer rights.

Assuming you can buy a replacement power supply yourself then that's going to be the upper limit of the refund you're looking at if you want to keep the phone.

As you've had a good chunk of use out of the power supply (a third of it's expected lifetime? half?) it may be less than that, so don't expect huge amounts.

Probably the most salient info for OP is via quoting directly from statutory legislation:

(2) If the consumer requires the trader to repair or replace the goods, the trader must—
(a) do so within a reasonable time and without significant inconvenience to the consumer, and
(b) bear any necessary costs incurred in doing so (including in particular the cost of any labour, materials or postage).

(3) The consumer cannot require the trader to repair or replace the goods if that remedy (the repair or the replacement)—
(a) is impossible, or
(b) is disproportionate compared to the other of those remedies.

So summary would be:
trader must be given oppo(sic)rtunity to repair or replace without causing OP (half Oppo!) significant inconvenience.
If trader chooses to refund instead, anything beyond pro-rata refund is a gesture of goodwill win.

OP: likely to be in your interest to know the current cost to replace the original charger and / or original cable,
plus which merchant(s) has immediately available stock,
then use that knowledge when discussing possible remedies.

Buy one from oppo cost you £20...