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I've been watching these Tekin 900 dynos sell from $70 up to $300. I found one toward the lower half of that price range and decided to snag it.
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The manual is here:

https://www.rc10talk.com/viewtopic.php?f=7&t=18724&p=494248


My reason for avoiding Tekin peak chargers BITD was because most of them required 12vdc power, which was inconvenient. Apparently that's the curse with this motor dyno too. I'm not eager to have a spare 12v lead acid battery sitting around, so I think that leaves me with sourcing a 300w or higher power converter. It seems like desktop computer power supplies have the output capacity, but would need some tinkering to get a usable output connection. There look to be some RV power supplies as options. Amazon has several cheap-o options, but I'd like to find something in a reputable brand. I don't know what brands would be good bets though. I'm certainly open to suggestions to research.

I bought my MRC Road Winner circa 1988, about 3 months before buying my first used Hornet. I had a cheap DC charger to charge my cheap battery for my MRC. I remember waiting for it to charge off of my mom's Dodge Caravan(Complete with wooden panels)cigarette lighter. It was like watching and waiting for water to boil! That is the entirety of my knowledge, but I look forward to seeing what happens. Killer score, sometimes you just gotta have it!

You can get a bench top, voltage regulated power supply for about $70. A motorcycle or lawn mower battery isn’t too big or messy…and the smooth DC power they supply may help with consistent readings. If you have a motorcycle or a riding lawn mower..maybe just buy an extra of whatever they take, so that the battery can be used in the future if you get bored with the dyno.

A modified server or ATX power supply might be an option. Most 500 watt units supply around 40 amps.

What about just using 3s lipo? If you don’t need to run the dyno for a long time even a modest capacity one will put out close enough to 12v.

It sounds like you don’t have. I have other use for a12v power supply or lead acid battery.

Most rc chargers will also charge a lead acid battery so one of those may be useful as well.

I hope this is a workable solution as a 12v DC, 40A capable power supply.
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This power supply was supposed to have different colored wires in the harness, but instead I was sent the model with all black wiring. Oh well, that just makes it more challenging to succeed.

Step 1 - remove the sticker that says Warranty is Void if Removed. Done
Step 2 - do something that really would void a warranty, like accidentally cut some wires to a motherboard connector while removing the wire loom. Done.
Step 3 - identify 12v + & - output ocations. Done.
Step 4 - plug in and test for power. Ugh, no 12v power.

Turning the power supply on and off does nothing right now. I see a green ended wire that is labeled PSON by it. That seems like it should be for a computer case power switch. But what that would should connect with to complete the circuit path and allow the power supply to come alive is less obvious right now.
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I used a large resistor on the 5V section to simulate load.

I was thinking I just needed to connect the PSON wire to something else in the power supply to enable it to power up. You're saying that instead a load on the 5V circuit would bring it to life without connecting anything to the PSON wire??

The purple ended wire is 5v standby and there's a ground wire next to it. Reading up a bit on ATX PSU operation on smpspowersupply.com

So, connecting a resistive load (like a 12v automotive lightbulb) to the PSON and PG wires did activate the main 5v and 12v circuits of the power supply. . Now I need to clean up the wiring rats nest and setup some safe 12v connection points for alligator clips.
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It's a 12v power supply now. The +12v and the -12v that come from the same circuit board locations are ganged together into single power leads. The others bundled by location, capped, and then bundled as a group of unused leads. The voltage it puts out with no load continuously varies from 11.9x to 12.1x volts. With a single bulb as a load the bulb has a varying intensity.
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Nice and clean.

After I test it with the dyno, if this works out as a 12v power supply I will go back in and remove the computer wiring stubs and just have the 2 power lines coming out of the case. But before I make any board soldering goofs I want to make sure it's a usable solution.

The Tekin Dyno doesn't seem to like this power supply. The power output keeps cycling between 11.98v and 12.17v and the Dyno test motor keeps increasing and dropping revs. I tried out a 14v 10a Novak N-power supply and I get a good steady motor RPM.
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