@RichJ 

The HS103 require the DNS be able to resolve the following addresses:

devs-gw.tplinkcloud.com 
deventry.tplinkcloud.com 

It seems the pi-hole is not doing that.

@Tony 

Both of these can be resolved before and after I added them to the whitelist in PiHole.  I added them to the whitelist with wildcard, meaning any subdomain is also whitelisted also.  Switched them back from 8.8.8.8 and rebooted them.   Still the same result. :-(

Any other ideas?

PS H:\> nslookup deventry.tplinkcloud.com 192.168.1.15
Server:  raspberrypi-1
Address:  192.168.1.15

Non-authoritative answer:
Name:    deventry.tplinkcloud.com
Addresses:  54.204.63.77
          3.216.21.164

PS H:\> nslookup devs-gw.tplinkcloud.com 192.168.1.15
Server:  raspberrypi-1
Address:  192.168.1.15

Non-authoritative answer:
Name:    use1-devs-gw.tplinkcloud.com
Addresses:  34.205.22.181
          52.206.116.115
          3.225.235.82
          34.204.115.126
          3.215.31.202
          34.205.86.210
          3.226.66.87
          50.19.49.116
Aliases:  devs-gw.tplinkcloud.com

PS H:\>

@RichJ 

Try one more cloud server name which is actually the default one:

devs.tplinkcloud.com

If that still does not work, please DM me the MAC address of your smart plug.

@Tony 

That one works also.

PS H:\> nslookup devs.tplinkcloud.com 192.168.1.15
Server:  raspberrypi-1
Address:  192.168.1.15

Non-authoritative answer:
Name:    prd-elb-connector-0-563583643.us-east-1.elb.amazonaws.com
Addresses:  34.199.227.235
          3.215.211.164
          3.224.235.192
          34.199.172.24
          34.225.47.234
          52.21.18.148
          3.211.201.183
          52.203.141.21
Aliases:  devs.tplinkcloud.com

PS H:\>

I don't understand it.  Something they're trying to get to obviously can't resolve.  :-/