I have a car pc based on a raspberry pi, runs on 5v @1a loaded

I built it around a small switch mode power supply that I poached from a dead gps, rated at 2 amps, its very efficient, low heat, and very clean output on the scope. similar to a cheap cellphone charger.

unfortunately it doesn't survive cranking sometimes. it produces output around 5v but the waveform is madly unstable and the car pc locks up

what would you do with minimal funds? this is for a low budget project that I want to be reproducable..

- build a linear mode supply instead? (don't want to due to heat/inefficient)
- try to put a shitload of caps on input? output? both? how big of caps?
- give up and buy a fancier switch mode supply that'll take a beating?