Replacing the parts

I could find the SS8050 and SS8550 at various resellers, however the usual ones only have TO-92 packages, not the SOT-23 variant.
(Digikey has them is SOT-23, but it's not the most convenient reseller for europe)

Anyhow it isn't a huge deal - NPN and PNP are quite common, and after some search and filtering, I found two equivalents :

FMMT619 and FMMT720

They are better than SS8X50 parts in pretty much all parameters.
A good idea to improve those as they might actually survive longer than the original parts.
The original parts are market Y1 and Y2

My replacement transistors are marked 720 and 619 on the package. (not shown here)

After replacing the four transistors, I powered up the device again and ... tada !
Fully working again.
Voltage now holds within 12-18V and stays there.

So definity, the SkyRC guys know their products.

If you ever wonder how crap the device is ... well it's not.
I rarely see power supplies of that quality coming from china.

Of course you could argue that it is a design flaw - and it might just be.

I haven't looked into the details, but just the input filtering is impressive.
Considering the amount of transformers, toroids and overall components is a good indicator of the quality.
They even invested in a high current sense resistor :

Most power supplies I see usually rely on the internal resistance of mosfets to measure current.
This works, but it's not very precise and pretty unreliable if the transistor is replaced by another brand/model for cost or repair reasons.

Those sense resistors are quite expensive and show the will to actually make a better than average product.

Well done SkyRC !