I should preface this post by saying that in my time I have serviced thousands of 6 volt AC points systems on two strokes ( Lambrettas specifically ), but my '78 DT125 currently has me pretty stumped. It all started when I swapped in a new condensor from one of those NGK tuneup kits in an effort to improve the spark and hopefully get rid of a slight misfire. I had previously installed the points from said kit and they had about 500 miles on them perhaps.

With the new condensor soldered in I was surprised to see absolutely no spark whatsoever.

I double checked with my meter set to Ohms that the points were breaking the field and not shorting out.

I also checked the voltage output of the stator at kickover across the black/white wire and the yellow one and saw close to 6v AC when giving it a good kick.

Next I took the coil off and took a trip to Kontiki Motorcycles where Alex bolted it up to another old 6v Yamaha and it threw fat blue sparks. Alex gave me another brand new 6v condensor to try, so in that went, making triple sure to check all wiring and connections for shorts, opens, etc. Still nothing.

"Oh wait, I don't recall seeing a ground wire from the frame to the engine ANYWHERE. That's got to be it!" I said to myself. So I put together a nice fat 8 gauge wire with two loop connectors and bolted that on. Once again, nothing.

Now I'm at the point where I'm ready to put the original condensor back in. Is it very likely that two brand new ones would be bad? In all my years servicing Lambrettas I can scarcely recall seeing any bad ones out of the box unless they were really, really old stock. Has quality control really gotten that bad, or is there something I'm missing?

With meter on Rx1 scale, what ohm readings do you get with points closed and points open?

Even without the condenser it will spark with plug sitting on the head, but won't under compression.
Points will arc but won't hurt just for a few kicks to check.
Can connect the condenser at the top coil directly into the coil 'in' wire if you have an aftermarket one with a mount tab to earth to the frame.
If it was running before i'm guessing there's something touching earth.
But if it was misfiring previously maybe the source coil has finally died.
Very unlikely scenario though.

In answer to the question in your thread title, yes, there are a lot of counterfeit condensers, coils, plugs and points out there.

In response to MarkT's question: "With meter on Rx1 scale, what ohm readings do you get with points closed and points open?"

I will do another test and get back to you on that. What kind of readings should I expect? I tested the points with them unbolted from the stator plate and they were breaking the field correctly (full continuity closed, 0 open).

In response to RT325:

"Even without the condenser it will spark with plug sitting on the head, but won't under compression.
Points will arc but won't hurt just for a few kicks to check.
Can connect the condenser at the top coil directly into the coil 'in' wire if you have an aftermarket one with a mount tab to earth to the frame.
If it was running before i'm guessing there's something touching earth.
But if it was misfiring previously maybe the source coil has finally died.
Very unlikely scenario though."'

I'm familiar with the externally mounted condensor test, though it will work only if the condensor has failed but not if there is a short in the ignition system. Then again the fact that I'm getting AC voltage from the stator tells me that there isn't a short and that the source coil is good, agree?

Zero ohms points closed (full no resistance connection to ground...  not to be confused with infinity indication of "0.L" that digital meters use to indicate an open circuit... )

Approximately one to two ohms with points open.  (can be difficult to get an accurate points open reading with many digital meters as most are "auto ranging" and jump around a lot)

Above is with one meter lead to ground and other connected to points wire with it disconnected from ignition coil.

Another common issue for no spark is a kill switch inadvertently off or bad which grounds out the points... (I get confused by the Yamaha handlebar switch sometimes and have it off when I think it's on.)

A jumper wire from points to small coil wire bypassing the harness is a quick way to test.  If you have spark with the jumper, then the harness or kill switches have a problem. 

Couple of short videos of mine from long ago.
Not sure what i was doing in the first one just showing points opening & closing.
Second shows ohms meter with points open & closed [or closed then open]. Ignore the meter not zeroing & call it zero where it goes to. That actually confused me initially until MarkT put me right.
My meter is old [like me] & won't adjust all the way on ohmsx1 scale.
Ignore the wire color, just a dodgy old totally reliable system source only & no lighting/charging coils.
Thought might help with you problem diagnosing it.
Hope the links work, been a long time.

youtube.com/shorts/pf2lPN8x_YI

youtube.com/shorts/qVm-uhxIAT4
I see i have the wire disconnected from the plug coil so i'm not sure if that fact alters the open points resistance but guess it does by an ohm or less for secondary primary windings. Regardless zero is still zero when points closed.
Help MarkT please!!, before i de-rail things.

Morley, you've likely forgotten more than most of us will ever know and you still know more than most of us!  Happy to have you here sharing your knowledge and experience helping us solve issues...  (I'm the one that needs help most of the time.)  

RT is far above and beyond any manual… he knows what wasn’t written between the lines… I sometimes wonder if the folks putting them together consult with him? (:  Mark T, you are a compliment to RT…  
lucky us!
Sneezles61