tranquilizer

I'll recommend this instead...
PCPartPicker Part List
CPU: AMD - Ryzen 5 2600 3.4 GHz 6-Core Processor  ($119.99 @ Newegg) 
Motherboard: ASRock - B450M PRO4 Micro ATX AM4 Motherboard  ($74.89 @ OutletPC) 
Memory: G.Skill - Aegis 16 GB (2 x 8 GB) DDR4-3000 Memory  ($52.99 @ Newegg Business) 
Storage: Mushkin - Source 500 GB 2.5" Solid State Drive  ($44.99 @ Newegg Business) 
Video Card: Sapphire - Radeon RX 570 4 GB PULSE Video Card  ($119.99 @ Newegg) 
Case: Deepcool - MATREXX 30 MicroATX Mini Tower Case  ($29.99 @ Newegg Business) 
Power Supply: Corsair - CX (2017) 450 W 80+ Bronze Certified ATX Power Supply  ($40.50 @ Newegg) 
Total: $483.34
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-07-19 04:45 EDT-0400

I'll recommend something like this instead...
Go fr the 2600 if you can afford it...
It's just £10 more...
 
PCPartPicker Part List
CPU: AMD - Ryzen 5 1600 3.2 GHz 6-Core Processor  (£105.59 @ Newegg UK) 
Motherboard: ASRock - X370M Pro4 Micro ATX AM4 Motherboard  (£59.69 @ Egenisys) 
Memory: Patriot - Viper 4 8 GB (2 x 4 GB) DDR4-3000 Memory  (£39.99 @ Amazon UK) 
Video Card: Gigabyte - Radeon RX 570 4 GB Gaming 4G  Video Card  (£119.46 @ Ebuyer) 
Total: £324.73
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-07-19 02:43 BST+0100

Wow, Almost completely right for once. 
 
In fact, you being right here shows how you were wrong earlier. Instead of recommendations by brand, you should suggest actual good units, so if OP picked a Seasonic Focus gold, which has crap transient response, your "critical phase" power draw would create problems, whereas a 550 watt unit with better transients, like a Corsair RMX, would not be an issue.

What do you mean by critical phase??
All the benchmarks are taken at peak loads, and while gaming you never hit those peak loads.

An i5 9400F does not consume a heavy amount of power. The RTX 2060 consumes around 175W max at stock, maybe up to around 225W when overclocked.
Even with overclocking the GPU (CPU is locked) you should be consuming less than 350W for the total system.
 
As far as wattage of the power supply goes, 550W would be plenty. 450w would also be acceptable.
 
Did you have any particular models of power supplies in mind that you were looking at? If not, what is your budget and we can recommend something.

A 550w PSU should be plenty considering it is of a decent quality.
I'll recommend CX/cxm series from Corsair or pure power 10/11 from be quiet or masterwatt series from cooler master. These are all 80+ bronze rated units.
 
If you want 80+ gold rated units, then I'll recommend RMx series from Corsair or MWE & masterwatt maker from cooler master or even focus plus/focus series from seasonic.
 
@Spotty can help you more in selecting a better power supply.
 
 

I'll recommend something like this instead...
 
PCPartPicker Part List
CPU: AMD - Ryzen 5 2600 3.4 GHz 6-Core Processor  ($119.99 @ Newegg) 
Motherboard: MSI - B450I GAMING PLUS AC Mini ITX AM4 Motherboard  ($129.97 @ Amazon) 
Memory: OLOy - 8 GB (1 x 8 GB) DDR4-3000 Memory  ($27.99 @ Newegg) 
Memory: OLOy - 8 GB (1 x 8 GB) DDR4-3000 Memory  ($27.99 @ Newegg) 
Storage: HP - EX920 512 GB M.2-2280 Solid State Drive  ($54.99 @ Newegg) 
Video Card: ASRock - Radeon RX 570 4 GB Phantom Gaming D Video Card  ($129.99 @ Newegg) 
Case: Silverstone - SG13 Mini ITX Tower Case  ($57.99 @ B&H) 
Power Supply: Corsair - CX (2017) 450 W 80+ Bronze Certified ATX Power Supply  ($40.40 @ OutletPC) 
Total: $589.31
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-07-17 02:03 EDT-0400