i5 8400 to i7 8700k

[Jonofre]

Im upgrading my cpu to an i7 8700k there's this really good deal, im running a gtx 1070. should i upgrade my psu while im at it? i have a 500w psu atm

 

[geofelt]

500w will run a GTX1070 just fine.

If your psu is of good quality, tier 1/2/3keep it.
https://linustechtips.com/main/topic/631048-psu-tier-list-updated/

Otherwise consider a quality 650w unit to allow for a future graphics card upgrade.
I like the Seasonic focus units.