NefMoto

I would like to do some experimental read/write to a spare ECU on the bench.

What are the requirements for a suitable powersupply, in terms of max. current? Am I better off with a spare 12V car battery?

Any regulated supply that provides 12 to 14 volts at with a current rating of at least 1 to 2 amps should be fine.
I think the key is that you want a regulated supply, not a standard "wall wart" that can have wildly varying voltage.

A computer power supply powered by a UPS would be my choice.

If you go the computer power supply route, you can use an ATX power supply if you short the green wire on the ATX connector to any of the black wires as your "turn on".  (I think the green wire is pin 14 IIRC). 

 I just use a small SLA 12v battery with a trickle charger on it since the spare PSU I tried had a low voltage output of like 11.89V

Thanx for the suggestions so far. Reliability is a top priority, price is second, but still a priority!

ATX power supply + UPS could do it, but an UPS is probably not cheap.

The SLA solution + trickle charger sounds good. And then I have a spare SLA if the one in the car let me down. Any idea to what happens, if the I experience a power outage during a flash, is the SLA sufficient to suppress any voltage spikes/drops?

Well, I was just making a wild assumption that anyone into computers enough to be flashing their own ECU's would have a UPS for their computer at home.

While the battery with trickle charger addresses a power outage, it does not do anything for voltage spikes. 

In all likelihood, either method will be fine, unless you are unlucky.

My notebook got an built-in UPS :-)

The trickle charger hasn't caused me any issues.  It is connected a small 4ah battery that you can buy at home depot/lowes for alarm systems/emergency lighting.

It's more prudent IMO to enable yourself to boot-mode flash in case of disaster.  Even with the cleanest, most voltage regulated power, you are still running the risk of windows blowing up when you flash and boot-mode is a fast and easy recovery method on the bench :)

For grins, I took a new seasonic 750watt PSU and chopped it up.  It provides a little over 12v with a load on it, and is very stable - did several boot mode flashes, reads, and then 10 back to back NefMoto reads/writes...  no issue.  So, perhaps my old PSU was just junk?  Either case, if you have a PSU laying around, try it.  Short the green wire on the ATX header to an adjacent black wire, and then connect power to it - it will power up.. give her a whirl!

Got one from radio shack, works great for bench flashing.

http://www.radioshack.com/product/index.jsp?productId=2103960&Camp=PPC%3AGoogle%3ATMProduct%3ABroad

I couldn't get reliable power from a few of the old ATX power supplies I used (from an old compaq & mac G4 tower). So I got this for around $20 shipped:

Pyramid PS3KX 3-Amp 12-Volt Power Supply (http://www.amazon.com/gp/product/B0002JTD2K/ref=as_li_ss_tl?ie=UTF8&tag=mattdannet-20&linkCode=as2&camp=217153&creative=399349&creativeASIN=B0002JTD2K)

What do you think about this guys? It will be good for bench flashing?

http://www.ebay.co.uk/itm/Mercury-650-656-Switch-Mode-13-8V-Bench-Top-Power-Supply-1-6m-Power-Lead-New-/131293693621?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item1e91b6c6b5

I use one of these: http://www.ebay.com/itm/Farnell-Instruments-Dual-Stabilized-Voltage-Power-Supply-LT30-2-220V-/301144489257?pt=LH_DefaultDomain_0&hash=item461d9c3d29

Overkill, but its nice having ammeter so you can see what the ecu is doing :)

Have good luck with this. Cheap and portable

http://laptopchargerfactory.com/syncmaster-150mp