Final ? About Coolpix 775 Charger:Voltage from Replacement AC Adaptor

I've posted 2 threads or more already regarding batteries, chargers etc with
my Nikon Coolpix 775. As I mentioned the camera & rechargeable batteries
themselves work fine. But the charger was dead on arrival.

This posting is sort of long, so to make it easier, the real meat of my
question is marked at the beginning of the paragraph with a (----HERE-----)
so you can see it easily visually.

The background:

The charger's cord is an AC Adapter-type of cord, and it's detachable.
Naturally, I thought--hey--if the adapter is what's dead, why not just
substitute another? Of course the voltage would have to be the same or close
to it. (Yes, I know--I could get a replacement from Nikon. But that would
take forever. Meanwhile, I either have to buy another charger--hard to find
except on eBay--and burn out lithiums while waiting.)

Turns out that IS what the problem was. I found another adaptor and plugged
it in, and voila--the charger light popped on. I also tried having it charge
the battery overnight. I get up this morning, and wouldn't you know it--the
battery was fully charged and powered the camera right up. (Now I'm going to
see how many shots I get out of it before I have to recharge.)

Naturally I had to make sure I matched up properly with regards to whether
the tip on the cord needed to be + or - (it was +). As the AC Adapter was
switchable in that regard as well as regard to voltage--the adapter is meant
to replace many others with regards to voltage and polarity of the tip--I
was easily able to switch it to having a positive tip.

(----HERE-----)The only remaining issue is the voltage, and sorry for taking
so long to getting around to it--that's the main issue of this post. The
voltage of the AC Adapter I'm using doesn't match exactly what the other one
was, although it's close. Apparently the original AC Adapter has a 10.5 V
output, then the charger has the same input voltage (obviously) with an 8.4
V output (the V for charging the battery I would guess). Well as you might
can imagine my universal AC adapter doesn't have 10.5V as an option; the
closest 2 it has are 9V or 12V. I used 9V. (It runs from 1.5V to 12V,
in--for the most part anyway--1.5V steps. It skips from 9V to 12V, though.)

My question is, should that voltage be close enough to do the job not just
last night but in the long run, without compromising the quality of the
battery over the long haul? Or should I **really** be using EXACTLY 10.5V?

LRH