Most universal holsters are nylon. In general, unless they have some sort of retention strap or flap, they provide very little retention.
I always suggest folks don't cheap out on a holster. Between the G26 and the SR9, you have approximately $1,000 worth of guns, and a typical range session would cost most folks around $50. Spending $50 - $80 for a holster specifically designed to hold your gun seems like a good investment.
If you've got to have a generic one size fits all holster, you may want to try the various Uncle Mikes nylon holsters, or the Tauga belt slides. I've seen Hickok45 with what looks like Bianchi or Don Hume semi-slide holster that he uses for a variety of guns, but that's just to hold the gun while he's shooting on his range. You could check MidwayUSA and Brownell's for those type of holsters, and most gun stores or big box outdoor stores carry them.